Electrochemical cells comprising porous structures comprising sulfur

ABSTRACT

The present invention relates to the use of porous structures comprising sulfur in electrochemical cells. Such materials may be useful, for example, in forming one or more electrodes in an electrochemical cell. For example, the systems and methods described herein may comprise the use of an electrode comprising a conductive porous support structure and a plurality of particles comprising sulfur (e.g., as an active species) substantially contained within the pores of the support structure. The inventors have unexpectedly discovered that, in some embodiments, the sizes of the pores within the porous support structure and/or the sizes of the particles within the pores can be tailored such that the contact between the electrolyte and the sulfur is enhanced, while the electrical conductivity and structural integrity of the electrode are maintained at sufficiently high levels to allow for effective operation of the cell. Also, the sizes of the pores within the porous support structures and/or the sizes of the particles within the pores can be selected such that any suitable ratio of sulfur to support material can be achieved while maintaining mechanical stability in the electrode. The inventors have also unexpectedly discovered that the use of porous support structures comprising certain materials (e.g., metals such as nickel) can lead to relatively large increases in cell performance. In some embodiments, methods for forming sulfur particles within pores of a porous support structure allow for a desired relationship between the particle size and pore size. The sizes of the pores within the porous support structure and/or the sizes of the particles within the pores can also be tailored such that the resulting electrode is able to withstand the application of an anisotropic force, while maintaining the structural integrity of the electrode.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/237,903, filed Aug. 28, 2009, andentitled “Electrochemical Cells Comprising Porous Structures ComprisingSulfur,” which is incorporated herein by reference in its entirety forall purposes.

FIELD OF INVENTION

The present invention relates to electrochemical cells, and morespecifically, to systems and methods involving electrochemical cellscomprising porous structures comprising sulfur.

BACKGROUND

A typical electrochemical cell includes a cathode and an anode whichparticipate in an electrochemical reaction. Generally, electrochemicalreactions are facilitated by an electrolyte, which can contain free ionsand can behave as an electrically conductive medium. The performance ofan electrochemical cell can be enhanced by increasing the amount ofcontact between an electrode active material and the electrolyte (e.g.,by employing porous electrodes), which can lead to an increase in therate of the electrochemical reaction within the cell. In addition, theperformance of an electrochemical cell can be enhanced by maintaining ahigh degree of electrical conductivity within the bulk of the electrodes(e.g., between an electrode active material and a support on which it isdeposited). Accordingly, systems and methods that increase the amount ofcontact between electrode active materials and electrolytes as well asincrease the electrical conductivity within the electrodes would bebeneficial.

SUMMARY OF THE INVENTION

The present invention relates to electrochemical cells, and morespecifically, to systems and methods involving electrochemical cellscomprising porous structures comprising sulfur. The subject matter ofthe present invention involves, in some cases, interrelated products,alternative solutions to a particular problem, and/or a plurality ofdifferent uses of one or more systems and/or articles.

In one aspect, a method is described. The method can comprise providinga metallic porous support structure comprising a plurality of pores,wherein the plurality of pores of the metallic porous support structuretogether define a total pore volume, and at least about 50% of the totalpore volume is defined by pores having cross-sectional diameters ofbetween about 0.1 microns and about 10 microns; and depositing anelectrode active material comprising sulfur within the pores of themetallic porous support structure.

In another aspect, an electrode is described. The electrode cancomprise, in some embodiments, a metallic porous support structurecomprising a plurality of pores; and a plurality of particles comprisingan electrode active material comprising sulfur substantially containedwithin the pores of the metallic porous support structure, wherein eachparticle of the plurality of particles has a maximum cross-sectionaldimension; each particle of the plurality of particles has a particlevolume, and the plurality of particles has a total particle volumedefined by the total of each of the individual particle volumes; and atleast about 50% of the total particle volume is occupied by particleshaving maximum cross-sectional dimensions of between about 0.1 micronsand about 10 microns.

The electrode can comprise, in some cases, a metallic porous supportstructure comprising a plurality of pores; and a plurality of particlescomprising an electrode active material comprising sulfur substantiallycontained within the pores of the metallic porous support structure,wherein the plurality of particles together defines a total quantity ofparticulate material, and wherein at least about 50% of the totalquantity of particulate material is made up of particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns.

In some instances, the electrode can comprise a metallic porous supportstructure comprising a plurality of pores; and an electrode activematerial comprising sulfur substantially contained within the pores ofthe metallic porous support structure, wherein each pore of theplurality of pores has a pore volume, and the plurality of pores has atotal pore volume defined by the total of each of the individual porevolumes; and at least about 50% of the total pore volume is occupied bypores having cross-sectional diameters of between about 0.1 microns andabout 10 microns.

The electrode can comprise, in some embodiments, a metallic poroussupport structure comprising a plurality of pores; and an electrodeactive material comprising sulfur substantially contained within thepores of the metallic porous support structure, wherein the plurality ofpores of the metallic porous support structure together define a totalpore volume, and at least about 50% of the total pore volume is definedby pores having cross-sectional diameters of between about 0.1 micronsand about 10 microns.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control. All patents and patentapplications disclosed herein are incorporated by reference in theirentirety for all purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 is a schematic illustration of an exemplary electrochemical cell;

FIG. 2 is a schematic illustration of an electrochemical cell, accordingto another set of embodiments;

FIG. 3 is a schematic illustration of an exemplary electrochemical cell;

FIGS. 4A-4B include scanning electron micrographs (SEMs) of exemplaryelectrodes;

FIGS. 5A-5B include (A) a plot of specific discharge capacity as afunction of the number of charge-discharge cycles and (B) a plot ofcapacity as a function of C-rate, according to one set of embodiments;

FIGS. 6A-6F include (A) a secondary electron image of a sulfur-carboncomposite, (B-C) X-ray spectral images of the composite in FIG. 6A, (D)a secondary electron image of a cross-section of a sulfur-carboncomposite, and (E-F) X-ray spectral images of the composite in FIG. 6D,according to one set of embodiments;

FIG. 7 includes a plot of specific discharge capacity as a function ofthe number of charge-discharge cycles, according to one set ofembodiments;

FIGS. 8A-8B include secondary electron images of electrodes, accordingto one set of embodiments;

FIGS. 9A-9F include X-ray spectral images outlining the distributions of(A) sulfur in a composite cathode, (B) carbon in a composite cathode,(C) aluminum in a composite cathode, (D) sulfur in a mechanically mixedcathode, (E) carbon in a mechanically mixed cathode, and (F) aluminum ina mechanically mixed cathode, according to one set of embodiments;

FIG. 10 includes a plot of specific discharge capacity as a function ofthe number of charge-discharge cycles for exemplary electrochemicalcells;

FIG. 11 includes an exemplary plot of percentage capacity as a functionof C-rate, according to one set of embodiments;

FIG. 12 includes, according to one set of embodiments, a plot of cathodethickness as a function of applied pressure; and

FIG. 13 includes an exemplary plot of specific discharge capacity as afunction of cycle number, according to some embodiments.

DETAILED DESCRIPTION

The present invention relates to the use of porous structures comprisingsulfur in electrochemical cells. Such materials may be useful, forexample, in forming one or more electrodes in an electrochemical cell.For example, the systems and methods described herein may comprise theuse of an electrode comprising a conductive porous support structure anda plurality of particles comprising sulfur (e.g., as an active species)substantially contained within the pores of the support structure. Theinventors have unexpectedly discovered that, in some embodiments, thesizes of the pores within the porous support structure and/or the sizesof the particles within the pores can be tailored such that the contactbetween the electrolyte and the sulfur is enhanced, while the electricalconductivity and structural integrity of the electrode are maintained atsufficiently high levels to allow for effective operation of the cell.Also, the sizes of the pores within the porous support structures and/orthe sizes of the particles within the pores can be selected such thatany suitable ratio of sulfur to support material can be achieved whilemaintaining mechanical stability in the electrode. The inventors havealso unexpectedly discovered that the use of porous support structurescomprising certain materials (e.g., metals such as nickel) can lead torelatively large increases in cell performance. In some embodiments,methods for forming particles comprising electrode active material(e.g., comprising sulfur) within pores of a porous support structureallow for a desired relationship between the particle size and poresize. The sizes of the pores within the porous support structure and/orthe sizes of the particles within the pores can also be tailored suchthat the resulting electrode is able to withstand the application of ananisotropic force, while maintaining the structural integrity of theelectrode.

In developing the systems and methods described herein, the inventorshave identified several challenges associated with producing electrodescomprising sulfur. First, sulfur possesses a relatively low electricalconductivity (e.g., about 5.0×10⁻¹⁴ S cm⁻¹ for elemental sulfur), whichcan inhibit the electrical conductivity of the electrode and hence, cellperformance. In addition, small particle sulfur, which can be useful inproducing uniform thickness and high surface-area electrodes, can bedifficult to produce using traditional mechanical milling, as theparticles that are produced can quickly re-agglomerate. Moreover, highsurface area carbon, which can yield relatively high specific capacityand cycle life, can be difficult to process as a traditional slurrybecause it possesses a high absorption stiffness resulting in a slurrywith a relatively low amount of solids. Finally, traditional slurryprocessing of sulfur-containing electrode materials can lead tore-distribution of the slurry components, which can produce unevenporosity within the cathode and decreased anode utilization. Theinventors have unexpectedly discovered that these traditionaldisadvantages can be overcome by disposing particles comprising sulfurwithin the pores of a support material to produce an electrode thatincludes relatively uniform porosity, particle size, and componentdistribution.

The porous structures described herein can be used in electrochemicalcells for a wide variety of devices, such as, for example, electricvehicles, load-leveling devices (e.g., for solar- or wind-based energyplatforms), portable electronic devices, and the like. In some cases,the porous structures described herein may be particularly useful aselectrodes in secondary batteries (i.e., rechargeable batteries) such aslithium-sulfur (L—S) batteries.

In one aspect, an electrode for use in an electrochemical cell isdescribed. The electrode may comprise a porous support structurecomprising a plurality of pores. As used herein, a “pore” refers to apore as measured using ASTM Standard Test D4284-07, and generally refersto a conduit, void, or passageway, at least a portion of which issurrounded by the medium in which the pore is formed such that acontinuous loop may be drawn around the pore while remaining within themedium. Generally, voids within a material that are completelysurrounded by the material (and thus, not accessible from outside thematerial, e.g. closed cells) are not considered pores within the contextof the invention. It should be understood that, in cases where thearticle comprises an agglomeration of particles, pores include both theinterparticle pores (i.e., those pores defined between particles whenthey are packed together, e.g. interstices) and intraparticle pores(i.e., those pores lying within the envelopes of the individualparticles). Pores may comprise any suitable cross-sectional shape suchas, for example, circular, elliptical, polygonal (e.g., rectangular,triangular, etc.), irregular, and the like.

The porous support structure can comprise any suitable form. In someinstances, the porous support structure can comprise a porousagglomeration of discreet particles, within which the particles can beporous or non-porous. For example, the porous support structure might beformed by mixing porous or non-porous particles with a binder to form aporous agglomeration. Electrode active material might be positionedwithin the interstices between the particles and/or the pores within theparticles (in cases where porous particles are employed) to form theinventive electrodes described herein.

In some embodiments, the porous support structure can be a “porouscontinuous” structure. A porous continuous structure, as used herein,refers to a continuous solid structure that contains pores within it,with relatively continuous surfaces between regions of the solid thatdefine the pores. Examples of porous continuous structures include, forexample, a piece of material that includes pores within its volume(e.g., a porous carbon particle, a metal foam, etc.). One of ordinaryskill in the art will be capable of differentiating between a porouscontinuous structure and, for example, a structure which is not a porouscontinuous structure but which is a porous agglomeration of discreetparticles (where the interstices and/or other voids between the discreteparticles would be considered pores) by, for example, comparing SEMimages of the two structures.

The porous support structure may be of any suitable shape or size. Forexample, the support structure can be a porous continuous particle withany suitable maximum cross-sectional dimension (e.g., less than about 10mm, less than about 1 mm, less than about 500 microns, etc.). In somecases, the porous support structure (porous continuous or otherwise) canhave a relatively large maximum cross-sectional dimension (e.g., atleast about 500 microns, at least about 1 mm, at least about 10 mm, atleast about 10 cm, between about 1 mm and about 50 cm, between about 10mm and about 50 cm, or between about 10 mm and about 10 cm). In someembodiments, the maximum cross-sectional dimension of a porous supportstructure within an electrode can be at least about 50%, at least about75%, at least about 90%, at least about 95%, at least about 98%, or atleast about 99% of the maximum cross sectional dimension of theelectrode formed using the porous continuous structure.

In some embodiments, the support structure can be an article with onerelatively thin dimension relative to the other two, such as, forexample, a film. For example, the support structure can be an articlewith a thickness of less than about 1 mm, less than about 500 microns,less than about 100 microns, between about 1 micron and about 5 mm,between about 1 micron and about 1 mm, between about 10 microns andabout 5 mm, or between about 10 microns and about 1 mm, and a widthand/or length at least about 100, at least about 1000, or at least about10,000 times greater. As used herein, the “maximum cross-sectionaldimension” of an article (e.g., a porous support structure) refers tothe largest distance between two opposed boundaries of an article thatmay be measured. Porous support structures described herein may also beof any suitable shape. For example, the support structure can bespherical, cylindrical, or prismatic (e.g., a triangular prism,rectangular prism, etc.). In some cases, the morphology of the supportstructure may be selected such that the support structure can berelatively easily integrated into an electrode for use in, for example,an electrochemical cell. For example, the support structure may comprisea thin film upon which additional components of an electrochemical cell(e.g., an electrolyte, another electrode, etc.) can be formed.

In some cases, porous particles can be used as a porous continuousstructure. In some such embodiments, material (e.g., electrode activematerial) can be deposited within the pores of the particles, and theparticles can be used to form an electrode. For example, porousparticles containing electrode active material within their pores mightbe bound together (e.g., using binder or other additives) to form acomposite electrode. Exemplary processes for forming such compositeelectrodes are described, for example, in U.S. Pub. No.: 2006/0115579,filed Jan. 13, 2006, entitled “Novel composite cathodes, electrochemicalcells comprising novel composite cathodes, and processes for fabricatingsame”, which is incorporated herein by reference in its entirety.

In some embodiments, the porous support structure might comprise arelatively large-scale porous continuous structure that, unlike theporous particles described above, is sized and shaped to serve as anelectrode. Such structures can be formed of a variety of materials suchas, for example, metals (e.g., a metal foam), ceramics, and polymers.Examples of such materials are described in more detail below. In someembodiments, the maximum cross-sectional dimension of a porouscontinuous structure within an electrode can be at least about 50%, atleast about 75%, at least about 90%, at least about 95%, at least about98%, or at least about 99% of the maximum cross sectional dimension ofthe electrode formed using the porous continuous structure.

The use of such relatively large porous continuous structures can, insome embodiments, ensure that little or no binder is located within theelectrode because binder would not be required to hold together smallparticles to form the porous support structure. In some embodiments, theelectrode can include less than about 20 wt %, less than about 10 wt %,less than about 5 wt %, less than about 2 wt %, less than about 1 wt %,or less than about 0.1 wt % binder. In this context, “binder” refers tomaterial that is not an electrode active material and is not included toprovide an electrically conductive pathway for the electrode. Forexample, an electrode might contain binder to facilitate internalcohesion within the cathode.

The porous support structure may comprise any suitable material. In someembodiments, the porous support structure can be used as an electricalconductor within the electrode (e.g., as an electrolyte-accessibleconductive material). Accordingly, the porous support structure maycomprise an electrically conductive material. Examples of electricallyconductive materials that may be suitable for use include, but are notlimited to, metals (e.g., nickel, copper, aluminum, iron, or any othersuitable metal or combination in pure or alloyed form), carbon (e.g.,graphite, carbon black, acetylene black, carbon fibers, carbonnanofibers, hallow carbon tubes, graphene, carbon filaments, etc.),electrically conductive polymers, or any other suitable electricallyconductive material. In some embodiments, the bulk of the porous supportstructure may be formed from an electrically conductive material. Insome cases, the porous support structure may comprise an electricallynon-conductive material that is at least partially coated (e.g., viasolution-based deposition, evaporative deposition, or any other suitabletechnique) with a conductive material. In some embodiments, the poroussupport structure may comprise a glass (e.g., silicon dioxide, amorphoussilica, etc.), a ceramic (e.g., aluminum oxide, tin oxide, vanadiumoxide, and others described below), a semiconductor (e.g., silicon,germanium, gallium arsenide, etc.), non-conductive polymers, and thelike.

The porous support structure may comprise pores with a size distributionchosen to enhance the performance of the electrochemical cell. In somecases, the porous support structure may comprise pores than are largerthan sub-nanometer scale and single-nanometer scale pores, which can betoo small to allow for the passage of electrolyte (e.g., liquidelectrolyte) into the pores of the electrode due to, for example,capillary forces. In addition, in some cases, the pores may be smallerthan millimeter-scale pores, which may be so large that they render theelectrode mechanically unstable. In some embodiments, the porous supportstructure can comprise a plurality of pores, wherein each pore of theplurality of pores has a pore volume, and the plurality of pores has atotal pore volume defined by the sum of each of the individual porevolumes. In some embodiments, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total pore volume is occupied by poreshaving cross-sectional diameters of between about 0.1 microns and about10 microns. In some embodiments, at least about 50%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, at leastabout 99%, or substantially all of the total pore volume is occupied bypores having cross-sectional diameters of between about 0.1 microns andabout 20 microns, between about 1 micron and about 10 microns, orbetween about 1 micron and about 3 microns. Stated another way, in someembodiments, the plurality of pores of the porous support structuretogether defines a total pore volume, and at least about 50% (or atleast about 70%, at least about 80%, at least about 90%, at least about95%, at least about 99%, or substantially all) of the total pore volumeis defined by pores having cross-sectional diameters of between about0.1 microns and about 10 microns (or between about 0.1 microns and about20 microns, between about 1 micron and about 10 microns, or betweenabout 1 micron and about 3 microns).

In some embodiments, it may be advantageous to use porous materialswherein the plurality of pores has an average cross-sectional diameterwithin a designated range. For example, in some cases, the poroussupport material may comprise a plurality of pores wherein the averagecross-sectional diameter of the plurality of pores is between about 0.1microns and about 10 microns, between about 1 micron and about 10microns, or between about 1 micron and about 3 microns.

As described below, the pore distributions described herein can beachieved, in some cases, while an anisotropic force (e.g., defining apressure of between about 4.9 Newtons/cm² and about 198 Newtons/cm², orany of the ranges outlined below) is applied to the electrochemicalcell. This can be accomplished by fabricating the porous supportstructure from materials (e.g., metals, ceramics, polymers, etc.)capable of maintaining their porosities under applied loads. Fabricatingan electrode from a material which resists deformation under an appliedload can allow the electrode to maintains its permeability underpressure, and allows the cathode to maintain the enhanced ratecapabilities described herein. In some embodiments, the yield strengthof the porous support structure (and the resulting electrode producedfrom the porous support structure) can be at least about 200Newtons/cm², at least about 350 Newtons/cm², or at least about 500Newtons/cm². Methods of fabricating such structures are described inmore detail below.

As used herein, the “cross-sectional diameter” of a pore refers to across-sectional diameter as measured using ASTM Standard Test D4284-07.The cross-sectional diameter can refer to the minimum diameter of thecross-section of the pore. The “average cross-sectional diameter” of aplurality of pores refers to the number average of the cross-sectionaldiameters of each of the plurality of the pores.

One of ordinary skill in the art would be capable of calculating thedistribution of cross-sectional diameters and the averagecross-sectional diameter of the pores within a porous structure usingmercury intrusion porosimetry as described in ASTM standard D4284-92,which is incorporated herein by reference in its entirety. For example,the methods described in ASTM standard D4284-92 can be used to produce adistribution of pore sizes plotted as the cumulative intruded porevolume as a function of pore diameter. To calculate the percentage ofthe total pore volume within the sample that is occupied by pores withina given range of pore diameters, one would: (1) calculate the area underthe curve that spans the given range over the x-axis, (2) divide thearea calculated in step (1) by the total area under the curve, and (3)multiply by 100%. Optionally, in cases where the article includes poresizes that lie outside the range of pore sizes that can be accuratelymeasured using ASTM standard D4284-92, porosimetry measurements may besupplemented using BET surface analysis, as described, for example, inS. Brunauer, P. H. Emmett, and E. Teller, J. Am. Chem. Soc., 1938, 60,309, which is incorporated herein by reference in its entirety.

In some embodiments, the porous material may comprise pores withrelatively uniform cross-sectional diameters. Not wishing to be bound byany theory, such uniformity may be useful in maintaining relativelyconsistent structural stability throughout the bulk of the porousmaterial. In addition, the ability to control the pore size to within arelatively narrow range can allow one to incorporate a large number ofpores that are large enough to allow for fluid penetration (e.g.,electrolyte penetration) while maintaining sufficiently small pores topreserve structural stability of the porous material. In someembodiments, the distribution of the cross-sectional diameters of thepores within the porous material can have a standard deviation of lessthan about 50%, less than about 25%, less than about 10%, less thanabout 5%, less than about 2%, or less than about 1% of the averagecross-sectional diameter of the plurality of pores. Standard deviation(lower-case sigma) is given its normal meaning in the art, and can becalculated as:

$\sigma = \sqrt{\frac{\sum\limits_{i = 1}^{n}\; \left( {D_{i} - D_{avg}} \right)^{2}}{n - 1}}$

wherein D_(i) is the cross-sectional diameter of pore i, D_(avg) is theaverage of the cross-sectional diameters of the plurality of pores, andn is the number of pores. The percentage comparisons between thestandard deviation and the average cross-sectional diameters of thepores outlined above can be obtained by dividing the standard deviationby the average and multiplying by 100%.

The electrodes described herein can also comprise a materialsubstantially contained within the pores of the porous supportstructure. A material that is said to be “substantially contained”within a pore is one that at least partially lies within the imaginaryvolume defined by the outer boundaries of the pore. For example, amaterial substantially contained within a pore can be fully containedwithin the pore, or may only have a fraction of its volume containedwithin the pore, but a substantial portion of the material, overall, iscontained within pores. In one set of embodiments, material (e.g.,material comprising sulfur) is provided, at least 30% of which by massis contained within pores of a porous support structure. In otherembodiments, at least 50%, 70%, 80%, 85%, 90%, or 95% by mass of thematerial is contained within the pores of the support structure.

The material within the support structure can comprise, in some cases,particles, which may be substantially solid or porous. In someembodiments, the material substantially contained within the pores maycomprise isolated particles or agglomerated particles. In someembodiments, the material may comprise a film (which may besubstantially solid or porous) on at least a portion of the pores withinthe support structure. In some embodiments, the material maysubstantially fill at least a portion of the pores within the supportstructure, such that the material assumes the shape and/or size of theportion of the pores.

The material within the support structure may comprise, in some cases,an electrode active material. As used herein, the term “electrode activematerial” refers to any electrochemically active species associated withan electrode. For example, a cathode active material refers to anyelectrochemically active species associated with the cathode, while ananode active material refers to any electrochemically active speciesassociated with an anode.

In some embodiments, the electrodes of the present invention maycomprise a relatively large amount of material comprising electrodeactive material within the pores of the porous support. For example, insome embodiments, the electrode (e.g., cathode) may comprise at leastabout 20 wt %, at least about 35 wt %, at least about 50 wt %, at leastabout 65 wt %, or at least about 75 wt % material comprising electrodeactive material, such as the electroactive sulfur-containing materialsdescribed herein.

The material within the pores of the porous support structure maycomprise a variety of compositions. In some embodiments, the materialwithin the pores can comprise sulfur. For example, the material withinthe pores can comprise electroactive sulfur-containing materials.“Electroactive sulfur-containing materials,” as used herein, refers toelectrode active materials which comprise the element sulfur in anyform, wherein the electrochemical activity involves the oxidation orreduction of sulfur atoms or moieties. As an example, the electroactivesulfur-containing material may comprise elemental sulfur (e.g., S₈). Inanother embodiment, the electroactive sulfur-containing materialcomprises a mixture of elemental sulfur and a sulfur-containing polymer.Thus, suitable electroactive sulfur-containing materials may include,but are not limited to, elemental sulfur, sulfides or polysulfides(e.g., of alkali metals) which may be organic or inorganic, and organicmaterials comprising sulfur atoms and carbon atoms, which may or may notbe polymeric. Suitable organic materials include, but are not limitedto, those further comprising heteroatoms, conductive polymer segments,composites, and conductive polymers.

In some embodiments, an electroactive sulfur-containing material of acathode active layer comprises at least about 40 wt % sulfur. In somecases, the electroactive sulfur-containing material comprises at leastabout 50 wt %, at least about 75 wt %, or at least about 90 wt % sulfur.

Examples of sulfur-containing polymers include those described in: U.S.Pat. Nos. 5,601,947 and 5,690,702 to Skotheim et al.; U.S. Pat. Nos.5,529,860 and 6,117,590 to Skotheim et al.; U.S. Pat. No. 6,201,100issued Mar. 13, 2001, to Gorkovenko et al. of the common assignee, andPCT Publication No. WO 99/33130. Other suitable electroactivesulfur-containing materials comprising polysulfide linkages aredescribed in U.S. Pat. No. 5,441,831 to Skotheim et al.; U.S. Pat. No.4,664,991 to Perichaud et al., and in U.S. Pat. Nos. 5,723,230,5,783,330, 5,792,575 and 5,882,819 to Naoi et al. Still further examplesof electroactive sulfur-containing materials include those comprisingdisulfide groups as described, for example in, U.S. Pat. No. 4,739,018to Armand et al.; U.S. Pat. Nos. 4,833,048 and 4,917,974, both to DeJonghe et al.; U.S. Pat. Nos. 5,162,175 and 5,516,598, both to Visco etal.; and U.S. Pat. No. 5,324,599 to Oyama et al.

While sulfur, as the active electrode species, is describedpredominately, it is to be understood that wherever sulfur is describedas the active electrode species herein, any suitable electrode activespecies may be used. Those of ordinary skill in the art will appreciatethis and will be able to select species (e.g., from the list describedbelow) for such use.

In embodiments in which the material within the pores comprisesparticles (e.g., particles of electrode active material), the particlescan be of any suitable shape. For example, in some embodiments, theparticles may be substantially spherical. In some cases, a particle canbe similar in shape to the pore it occupies (e.g., cylindrical,prismatic, etc.).

The size of the particles (e.g., particles of electrode active material)within the pores of the porous support structure can be selected toenhance the performance of the electrochemical cell. In someembodiments, each particle of the plurality of particles within thepores of the porous support structure has a particle volume, and theplurality of particles has a total particle volume defined by the sum ofeach of the individual particle volumes. In addition, in someembodiments, each particle of the plurality of particles within thepores of the porous support structure has a maximum cross-sectionaldimension. In some instances, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total particle volume within the poresof the porous support structure is occupied by particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns. In some embodiments, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total particle volume within the poresof the porous support structure is occupied by particles having maximumcross-sectional dimensions of between about 1 micron and about 10microns, or between about 1 micron and about 3 microns. Stated anotherway, in some embodiments, the plurality of particles together defines atotal quantity of particulate material, and at least about 50% (or atleast about 70%, at least about 80%, at least about 90%, at least about95%, at least about 99%, or substantially all) of the total quantity ofparticulate material is made up of particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns (or between about 1 micron and about 10 microns, or betweenabout 1 micron and about 3 microns).

As used herein, the “maximum cross-sectional dimension” of a particlerefers to the largest distance between two opposed boundaries of anindividual particle that may be measured. The “average maximumcross-sectional dimension” of a plurality of particles refers to thenumber average of the maximum cross-sectional dimensions of theplurality of particles.

One of ordinary skill in the art would be capable of measuring themaximum cross-sectional dimension of a particle by, for example,analyzing a scanning electron micrograph (SEM) of a particle. Inembodiments comprising agglomerated particles, the particles should beconsidered separately when determining the maximum cross-sectionaldimensions. The measurement could be performed by establishing imaginaryboundaries between each of the agglomerated particles, and measuring themaximum cross-sectional dimension of the hypothetical, individuatedparticles that result from establishing such boundaries. Thedistribution of maximum cross-sectional dimensions and particle volumescould also be determined by one of ordinary skill in the art using SEManalysis. The total particle volume of the particles within the porescould be determined by one of ordinary skill in the art by employingmercury intrusion porosimetry according to ASTM Standard Test D4284-07(optionally with BET surface analysis) to measure the volume within thepores before and after the particles are disposed within the pores. Whenthe material inside the pores of the support structure is itself porous,mercury intrusion porosimetry measurements (with optional BET surfaceanalysis) may be supplemented with visual analysis of SEM micrographs todetermine the volume occupied by the material (e.g., particles) withinthe pores.

In some embodiments, the particles of material (e.g., electrode activematerial) within the porous support structure may have an averagemaximum cross-sectional dimension within a designated range. Forexample, in some cases, the particles of material (e.g., electrodeactive material) within the porous support structure can have an averagemaximum cross-sectional dimension of between about 0.1 microns and about10 microns, between about 1 micron and about 10 microns, or betweenabout 1 micron and about 3 microns. In some embodiments, the ratio ofthe average maximum cross-sectional dimension of the particles ofmaterial within the porous support structure to the averagecross-sectional diameter of the pores within the porous supportstructure can be between about 0.001:1 and about 1:1, between about0.01:1 and about 1:1, or between about 0.1:1.

In some embodiments, particles within the pores of the porous supportstructure can have relatively uniform maximum cross-sectionaldimensions. Not wishing to be bound by any theory, such uniformity maybe useful in producing relatively consistent performance along a surfaceof an electrode comprising electrode active material particles. In someembodiments, the distribution of the cross-sectional dimensions of thepores within the porous material can have a standard deviation of lessthan about 50%, less than about 25%, less than about 10%, less thanabout 5%, less than about 2%, or less than about 1% of the averagecross-sectional diameter of the plurality of pores. Standard deviation(lower-case sigma) is given its normal meaning in the art, and can becalculated, and expressed as a percentage relative to an average, asdescribed above.

In some embodiments, the material (e.g., particles) within the pores ofthe porous support structure may occupy a relatively large percentage ofthe pore volume. For example, in some embodiments, the material withinthe porous support structure (e.g., particles comprising an electrodeactive material) can occupy at least about 10%, at least about 20%, atleast about 35%, at least about 50%, at least about 70%, or more of theaccessible pore volume of the porous support structure. As used herein,the “accessible pore volume” is consistent with the above definition ofa pore and refers to the percentage of the pore volume that is exposedto the external environment surrounding a porous article, as opposed topore volume that is completely enclosed by the material forming theporous article. The volume occupied by material within the pores shouldbe understood to include an imaginary volume that surrounds the outerboundaries of the material (e.g., particles) within the pores, which mayinclude material (e.g. particle) void volume in cases where the materialwithin the pores is itself porous. One of ordinary skill in the art iscapable of calculating the percentage of accessible pore volume, forexample, using mercury intrusion porosimetry measurements according toASTM Standard Test D4284-07, optionally supplemented by BET surfaceanalysis. The percentage of accessible pore volume within a porousarticle that is occupied by particles can be calculated, for example, byperforming mercury intrusion porosimetry measurements (optionally withBET surface analysis) of the porous article before and after theparticles are positioned within the pores. When the material inside thepores of the support structure is itself porous, mercury intrusionporosimetry measurements (with optional BET surface analysis) may besupplemented with visual analysis of SEM micrographs to determine thevolume occupied by the material (e.g., particles) within the pores.

The electrodes comprising the porous support structure may comprise arelatively high percentage of electrode active material (e.g., sulfur),in some cases. In some embodiments, the electrodes comprising the poroussupport structure can comprise, for example, at least about 20 wt %, atleast about 30 wt %, at least about 40 wt %, or more electrode activematerial. It should be understood that, for the purposes of calculatingthe amount of electrode active material within an electrode, only theweight of the electrode active species is counted. For example, in caseswhere electroactive sulfur-containing materials such as polysilfides ororganic materials comprising sulfur, only the sulfur content of theelectroactive sulfur-containing materials is counted in determining thepercentage of electrode active material within the electrode. In someembodiments, the electrodes comprising the porous support structure cancomprise at least about 20 wt %, at least about 30 wt %, at least about40 wt %, or more sulfur.

The electrodes described herein can comprise any suitable weight ratioof electrode active material and support material (e.g., any suitableratio of sulfur to carbon). For example, in some embodiments, theelectrode can comprise a weight ratio of sulfur to carbon of at leastabout 1:1, at least about 2:1, at least about 3:1, at least about 4:1,at least about 5:1, or at least about 6:1. In some embodiments, theelectrode can comprise a weight ratio of sulfur to carbon of less thanabout 6:1, less than about 5:1, less than about 4:1, less than about3:1, less than about 2:1, or less than about 1:1.

In some cases, the concentration of the electrode active material (e.g.,sulfur within a cathode) can be relatively consistent across one or moresurfaces of the electrode, or across any cross-section of the electrode.In some embodiments, at least about 50%, at least about 75%, at leastabout 85%, at least about 90%, at least about 95%, or at least about 98%of the area of the surface of an electrode (e.g., cathode) defines auniform area that includes a uniform distribution of electrode activematerial (e.g., sulfur). In some embodiments, at least about 50%, atleast about 75%, at least about 85%, at least about 90%, at least about95%, or at least about 98% of the area of a surface of a cross-sectionsubstantially perpendicular to the thickness of an electrode (e.g., acathode) defines a uniform area that includes a uniform distribution ofelectrode active material (e.g., sulfur).

In this context, a “surface of an electrode” refers to the geometricsurface of the electrode, which will be understood by those of ordinaryskill in the art to refer to the surface defining the outer boundariesof the electrode, for example, the area that may be measured by amacroscopic measuring tool (e.g., a ruler) and does not include theinternal surface area (e.g., area within pores of a porous material suchas a foam, or surface area of those fibers of a mesh that are containedwithin the mesh and do not define the outer boundary, etc.). Inaddition, a “cross-section of an electrode” defines an approximate planeviewed by cutting (actually or theoretically) the electrode to exposethe portion one wishes to analyze. After the electrode has been cut toobserve the cross-section, the “surface of the cross-section of theelectrode” corresponds to the exposed geometric surface. Stated anotherway, “surface of an electrode” and “surface of the cross-section of theelectrode” refer, respectively, to the geometric surface of theelectrode and the geometric surface of a cross-section of the electrode.

In some embodiments, an electrode active material (e.g., sulfur) isuniformly distributed when any continuous area that covers about 10%,about 5%, about 2%, or about 1% of the uniform area (described in thepreceding paragraphs) includes an average concentration of the electrodeactive material (e.g., sulfur) that varies by less than about 25%, lessthan about 10%, less than about 5%, less than about 2%, or less thanabout 1% relative to the average concentration of the electrode activematerial (e.g., sulfur) across the entirety of the uniform area. In thiscontext, the “average concentration” of an electrode active materialrefers to the percentage of the surface area of the electrode (e.g.,exposed surface area, surface area of a cross section of the electrode)that is occupied by electrode active material when the electrode isviewed from an angle substantially perpendicularly to the electrode.

One of ordinary skill in the art would be capable of calculating averageelectrode active material concentrations within a surface or across-section of an electrode, and the variance in concentrations, byanalyzing, for example, X-ray spectral images of an electrode surface orcross-section. For example, one could obtain an x-ray spectral image ofan electrode surface or cross-section (e.g., by physically slicing theelectrode to produce the cross-section), such as the images shown inFIGS. E6A-E6C. To calculate the average concentration of sulfur over agiven area in such an image, one would determine the percentage of theimage that is occupied by the color corresponding to sulfur over thatarea. To determine whether the average concentration within a sub-areavaries by more than X % relative to the average concentration within alarger area, one would use the following formula:

${{Variance}(\%)} = {{{\frac{C_{L} - C_{sub}}{C_{L}}} \cdot 100}\%}$

wherein C_(L) is the average concentration within the larger area(expressed as a percentage), C_(sub) is the average concentration withinthe sub-area (expressed as a percentage). As a specific example, if theaverage concentration of the electrode active material within a sub-areais 12%, and the average concentration of the electrode active materialwithin a larger area is 20%, the variance would be 40%.

Stated another way, in some embodiments, at least about 50% (or at leastabout 75%, at least about 85%, at least about 90%, at least about 95%,or at least about 98%) of the area of the surface of the electrode (orof a cross-section of the electrode) defines a first, continuous area ofessentially uniform sulfur distribution, the first area having a firstaverage concentration of sulfur. In some cases, any continuous area thatcovers about 10% (or about 5%, about 2%, or about 1%) of the first,continuous area of the surface of the electrode (or of the cross sectionof the electrode) includes a second average concentration of sulfur thatvaries by less than about 25% (or less than about 10%, less than about5%, less than about 2%, or less than about 1%) relative to the firstaverage concentration of sulfur across the first, continuous area.

In another aspect, a method of making an electrode for use in anelectrochemical cell is described. The method may comprise, in someembodiments, depositing a material (e.g., particles) substantiallywithin the pores of a porous support structure. The material depositedin the pores of the porous support structure can comprise an electrodeactive material such as, for example, sulfur. The porous supportstructure and the material can possess any of the characteristics (e.g.,materials, sizes, porosities, etc.) described herein.

Porous support structures (and resulting electrodes) can be fabricatedusing a variety of methods. For example, in some embodiments, particlescan be suspended in a fluid, and the fluid can be subsequently removed(e.g., via heat drying, vacuum drying, filtration, etc) to produce theporous support structure in which the particles are adhered to eachother. As mentioned above, in some cases, a binder can be used to adhereparticles to form a composite porous support structure.

In some embodiments, porous support structures can be fabricated byheating individual particles of a material until the particles arealtered to form a porous support structure (e.g., a porous continuousstructure). In some embodiments, particles (e.g., metallic particles,ceramic particles, glass particles, etc.) can be arranged such that theyare in contact with each other, with interstices located between theparticles. The particles can then be sintered to form a fused structurein which the interstices between the particles constitute the pores inthe sintered structure. As used herein, “sintering” is given its normalmeaning in the art, and is used to refer to a method for making objectsfrom particles, by heating the particles below their melting point untilthe particles adhere to each other. The total porosity, size of thepores, and other properties of the final structure could be controlledby selecting appropriate particles sizes and shapes, arranging them toform a desired packing density prior to sintering, and selectingappropriate sintering conditions (e.g., heating time, temperature,etc.).

In some cases, particles (e.g., polymeric particles, metallic particles,glass particles, ceramic particles, etc.) particles arranged such thatthey are in contact with each other can be heated such that theparticles melt to form a porous continuous structure. The interstices ofthe original structure can form the pores of the porous continuousstructure in some such embodiments. The total porosity, size of thepores, and other properties of the final structure could be controlledby selecting appropriate particles sizes and shapes, arranging them toform a desired packing density prior to heating, and selectingappropriate heating conditions (e.g., heating time, temperature, etc.).

In some embodiments, the particles can be controllably arranged prior tomelting or sintering. For example, in some cases in which the particlesare used to form a porous layer, it can be advantageous to arrange theparticles such that they are distributed relatively evenly andrelatively flatly against a substrate. This can be achieved, forexample, by suspending the particles in a solvent that is volatile(e.g., at room temperature), and pouring the solvent onto the substrateon which the porous structure is to be formed. After the particlesolvent is deposited, the volatile solvent can be allowed to evaporate,leaving behind a relatively well-ordered array of particles.

The sintering and/or melting processes described herein can be carriedout in a controlled atmosphere, in some cases. For example, the volumein which melting or sintering is performed can be filled with arelatively inter gas (e.g., nitrogen, argon, helium, and the like), insome cases. In some instances, the melting and/or sintering can becarried out in the substantial absence of oxygen, which can reduce oreliminate oxidation and/or combustion of the material used to form theporous support structure. In some embodiments, a reducing atmosphere(e.g., forming gas with the balance nitrogen and/or argon, hydrogen, orthe like) can be used to reduce the final oxygen content of the sinteredand/or melted article.

The sintering and/or melting temperature can be selected based upon thematerial being used to form the porous support structure. For example,when melting particles to form the porous support structure, the heatingtemperature can be selected such that it is above the meltingtemperature of the material from which the particles are made. One ofordinary skill in the art would be capable of selecting an appropriatesintering temperature, based upon the type of material being sintered.For example, suitable sintering temperatures for nickel might be betweenabout 700° C. and about 950° C.

As mentioned above, the sizes and shapes of the particles used to formthe porous support structure can be selected to achieve a desiredporosity. In some embodiments, the particles can be substantiallyspherical, although particles with other cross-sectional shapes (e.g.,ellipses, polygons (e.g., rectangles, triangles, squares, etc.),irregular, etc.) can also be used. The particles can be relatively small(e.g., in the form of a powder), in some embodiments. For example, insome cases, at least about 50%, at least about 70%, at least about 80%,at least about 90%, at least about 95%, at least about 99%, orsubstantially all of the particles have maximum cross-sectionaldimensions of between about 0.5 microns and about 20 microns or betweenabout 3 microns and about 5 microns. Such particle sizes can be usefulin producing porous support structures with the advantageous porosityproperties described elsewhere in this application.

In some embodiments, the porous support structure can be formed bycombining a first material with a second material, and forming the poresof the support structure by removing one of the materials from themixture. Removing one of the materials from the mixture can leave behindvoids which ultimately form the pores of the porous support structure.In some cases, the structure of the non-removed material can besubstantially maintained while one or more of the materials within themixture is removed. For example, in some cases, the support structurematerial (e.g., a metal, ceramic, glass, polymer, etc. which might bemelted) or a precursor to the support structure material (e.g., whichmight be converted to form the material of the porous support structurevia, for example, a reaction (e.g., polymerization, precipitation,etc.)), can be mixed with a plurality of templating entities. Thetemplating entities can be arranged such that they form aninterconnected network within the support structure material orprecursor. After the templating entities have been arranged within thesupport structure material, they can be removed from the supportstructure material to leave behind pores. The support structure materialcan be hardened before the templating entities are removed and/or duringthe removal of the templating entities. As used herein, the term“hardened” is used to refer to the process of substantially increasingthe viscosity of a material, and is not necessarily limited tosolidifying a material (although in one set of embodiments, a poroussupport structure material is hardened by converting it into a solid). Amaterial can be hardened, for example, by gelling a liquid phase. Insome instances, a material can be hardened using polymerization (e.g.,IR- or UV-induced polymerization). In some cases, a material can beinghardened can go through a phase change (e.g., reducing the temperatureof a material below its freezing point or below its glass transitiontemperature). A material may also be hardened by removing a solvent froma solution, for example, by evaporation of a solvent phase, therebyleaving behind a solid phase material.

The templating entities can be of any suitable phase. In some cases, thetemplating entities can be solid particles. For example, the templatingentities might comprise silica particles, which can be dissolved out ofa porous structure using, for example, hydrofluoric acid. As anotherexample, the templating entities might comprise ammonium bicarbonate,which can be removed by dissolving it in water. In some embodiments, thetemplating entities can comprise fluid (e.g., liquid and/or gas)bubbles.

The templating entities can also have any suitable shape, regular orirregular, including, but not limited to, spheres, cubes, pyramids, or amixture of these and/or other shapes. The templating entities may alsoeach be formed of any suitable size. In some embodiments, the templatingentities may have an average maximum cross-sectional dimension roughlyequivalent to the size of the desired pores within the porous supportstructure.

As a specific example, a metallic porous support structure can befabricated using metal injection molding. In an exemplary process, a“green” of metal particles, binder, and templating entities can beformed into a suitable structure (e.g., a relatively thin sheet) viainjection molding. As the green is heated, the metal particles can bemelted or sintered together while the binder and templating entities canbe burned off, leaving behind a series of pores.

Porous ceramic structures can also be produced using a templatingmethods. For example, in some cases, a ceramic foam can be produced byincluding ceramic particles and templating entities within a polyaphronsolution (i.e., a bi-liquid foam). The resulting mixture can be used ina sol gel solution, which can form a stable emulsion with the use of,for example, appropriate surfactants. Once the gel has been hardened,the templating entities can be removed by heat treatment. The size ofthe polyaphrons can be controlled by varying the type and amount of thesurfactants in the bi-liquid foam.

Templating methods can also be used to produce porous polymericstructures. For example, a plurality of solid particles might bedispersed within a monomer solution. After the monomer is polymerized toform a polymer, the solid particles can be selectively dissolved out ofthe mixture to leave behind a series of pores within the rest of thepolymeric structure.

Another method that might be used to produce the porous supportstructures described herein includes 3D printing. 3D printing is knownto those of ordinary skill in the art, and refers to a process by whicha three dimensional object is created by shaping successive layers,which are adhered on top of each other to form the final object. 3Dprinting can be used with a variety of materials, including metals,polymers, ceramics, and others.

A variety of materials (e.g., in particle form, in melt form, or otherforms mentioned herein) can be used to form the porous supportstructure. The material used to form all or part of the porous supportstructure can include a metal or a metal alloy, in some embodiments.Suitable metals include, but are not limited to, nickel, copper,magnesium, aluminum, titanium, scandium, and alloys and/or combinationsof these. In some embodiments, the metal or metal alloy from which theparticles are formed can have a density of less than about 9 g/cm³ orless than about 4.5 g/cm³.

In some embodiments, a polymeric material can be used to form all orpart of the porous support structure. Suitable polymers for use informing porous support structures include, but are not limited to,polyvinyl alcohol (PVA), phenolic resins (novolac/resorcinol), lithiumpolystyrenesulfonate (LiPSS), epoxies, UHMWPE, PTFE, PVDF, PTFE/vinylcopolymers, co-polymers/block co-polymers of the above and others. Insome embodiments, two polymers can be used for their uniquefuncionalities (e.g. PVA for adhesion, and LiPSS for rigidity, orresorcinol for rigidity and an elastomer for flexibility/toughness). Thematerial used to form the porous support structure might include one ormore conductive polymers such as, for example,poly(3,4-ethylenedioxythiphene) (PEDOT), poly(methylenedioxythiophene)(PMDOT), other thiophenes, polyaniline (PANI), polypyrrole (PPy). Thoseof ordinary skill in the art would be capable of selecting a counter ionfor a conductive polymer system, which can be selected from a variety ofchemical species such as PSS for PEDOT, other well known conductivepolymers, and co and block co-polymers as above.

A ceramic material might be used to form all or part of a porous supportstructure, in some instances. Suitable ceramics include, but are notlimited to, oxides, nitrides, and/or oxynitrides of aluminum, silicon,zinc, tin, vanadium, zirconium, magnesium, indium, and alloys thereof.In some cases, the porous support structure can include any of theoxides, nitrides, and/or oxynitrides above doped to impart desirableproperties, such as electrical conductivity; specific examples of suchdoped materials include tin oxide doped with indium and zinc oxide dopedwith aluminum. The material used to form the porous support structurecan comprise glass (e.g., quartz, amorphous silica, chalcogenides,and/or other conductive glasses) in some embodiments. The porous supportstructure can include, in some cases, aerogels and/or xero gels of anyof the above materials. In some cases, the porous support structure caninclude a vitreous ceramic.

In some embodiments in which the bulk of the porous support structure ismade of a material that is substantially electrically non-conductive,electrically conductive material can be deposited within the pores ofthe support structure to impart electrical conductivity. For example,the bulk of the porous support structure might comprise a ceramic (e.g.,glass) or an electrically non-conductive polymer, and a metal might bedeposited within the pores of the support structure. The electricallyconductive material can be deposited, for example, via electrochemicaldeposition, chemical vapor deposition, or physical vapor deposition. Insome cases, after the deposition of the electrically conductivematerial, an electrode active material can be deposited within the poresof the porous support structure. Suitable materials for placement withinthe pores of the porous support structure to impart electricalconductivity include, but are not limited to carbon and metals such asnickel and copper, and combinations of these.

The bulk of the porous support structure can be made electricallyconductive, in some embodiments, by incorporating one or moreelectrically conductive materials into the bulk of the porous supportstructure material. For example, carbon (e.g., carbon black, graphite orgraphene, carbon fibers, etc.), metal particles, or other electricallyconductive materials might be incorporated into a melt (e.g., anon-conductive polymeric melt, a glass melt, etc.) which is used to forma polymeric porous support structure to impart electrical conductivityto the porous support structure. After the melt is hardened, theelectrically conductive material can be included within the bulk of theporous support structure.

The mechanical properties of the porous support structure can also beenhanced by incorporating materials that structurally reinforce theporous support structure into the bulk of the porous support structure.For example, carbon fibers and/or particulate fillers can beincorporated into a melt (e.g., a metallic melt, a glass melt, apolymeric melt, etc.) which is hardened to form a porous supportstructure. In some cases, carbon fibers and/or particulate fillers canbe incorporated into a solution in which the porous support structure isformed (e.g., in some cases in which the porous support structurecomprises a polymer).

In some embodiments, the surfaces on or within of the porous supportstructure may be activated or modified prior to depositing the material,for example, to provide for enhanced attachment of material to thesurfaces of the porous support structure. Porous support structures canbe activated or modified by exposing the porous material to reactive orunreactive gasses or vapors. In some embodiments, the activation ormodification steps can be performed at elevated temperatures (e.g., atleast about 50° C., at least about 100° C., at least about 250° C., atleast about 500° C., at least about 750° C., or higher) and/orsub-atmospheric pressures (e.g., less than about 760 torr, less thanabout 250 torr, less than about 100 ton, less than about 10 torr, lessthan about 1 ton, less than about 0.1 ton, less than about 0.01 ton, orlower).

Electrode active material (e.g., particles, films, or other formscomprising electrode active material) may be deposited within the poresof the porous support structure via a variety of methods. In someembodiments, electrode active material is deposited by suspending ordissolving a particle precursor (e.g., a precursor salt, elementalprecursor material such as elemental sulfur, and the like) in a solventand exposing the porous support structure to the suspension or solution(e.g., via dipping the porous support structure into the solvent, byspraying the solvent into the pores of the porous support structure, andthe like). The particle precursor may subsequently form particles withinthe pores of the support structure. For example, in some cases, theprecursor may form crystals within the pores of the support structure.Any suitable solvent or suspension medium may be used in conjunctionwith such a technique including aqueous liquids, non-aqueous liquids,and mixtures thereof. Examples of suitable solvents or suspension mediainclude, but are not limited to, water, methanol, ethanol, isopropanol,propanol, butanol, tetrahydrofuran, dimethoxyethane, acetone, toluene,xylene, acetonitrile, cyclohexane, and mixtures thereof. Of course,other suitable solvents or suspension media can also be used as needed.

Electrode active material can also be deposited within the pores of thesupport structure, in some cases, by heating a material above itsmelting point or boiling point (optionally adjusting the surroundingpressure to, for example, aid in evaporation). The heated material maythen be flowed or vaporized into the pores of the support material suchthat particulate deposits or other solids are formed. As a specificexample, elemental sulfur powder can be positioned next to a poroussupport material and heated above the melting point of sulfur, such thatthe sulfur flows into the pores of the material (e.g., via sublimation,via liquid flow). The composite can then be cooled such that the sulfurdeposits within the pores.

In some embodiments, electrode active material can be deposited withinthe pores of the support structure via electrochemical deposition,chemical vapor deposition, or physical vapor deposition. For example,metals such as aluminum, nickel, iron, titanium, and the like, can beelectrochemically deposited within the pores of a porous supportstructure. Alternatively, such materials may be deposited, for example,using a physical vapor deposition technique such as, for example,electron beam deposition.

In some embodiments, catalyst may be deposited within the pores of thesupport structure in addition to the electrode active material (e.g.,before or during the deposition of the electrode active material). Insome cases, the catalyst may catalyze the electrochemical conversion ofthe electrode active material (e.g., the conversion of sulfur to Li₂Sand/or the conversion of Li₂S to sulfur). Suitable catalyst can include,for example, cobalt phthalocyanine and transition metal salts,complexes, and oxides (e.g., Mg_(0.6)Ni_(0.4)O).

The electrodes described herein may comprise one or more advantageousproperties. In some embodiments, the electrode may exhibit a relativelyhigh porosity. In some cases, the porosity of the electrode may be atleast about 30%, at least about 40%, at least about 50%, at least about60%, at least about 70%, at least about 80%, or at least about 90%. Suchporosities (and any of the pore distributions described herein) may beachieved, in some cases, while an anisotropic force (e.g., defining apressure of between about 4.9 Newtons/cm² and about 198 Newtons/cm², orany of the ranges outlined below) is applied to the electrochemicalcell. As used herein, the percentage porosity of an electrode (e.g., thecathode) is defined as the void volume of the electrode divided by thevolume within the outer boundary of the electrode, expressed as apercentage. “Void volume” is used to refer to portions of an electrodethat are not occupied by electrode active material (e.g., sulfur),conductive material (e.g., carbon, metal, etc.), binder, or othermaterials that provide structural support. The void volume within theelectrode may comprise pores in the electrode as well as intersticesbetween aggregates of the electrode material. Void volume may beoccupied by electrolyte, gases, or other non-electrode materials. Insome embodiments, the void volume of the electrode may be at least about1, at least about 2, at least about 4, or at least about 8 cm³ per gramof electrode active material (e.g., sulfur) in the electrode.

In some embodiments, the electrode can comprise a relatively largeelectrolyte accessible conductive material area. As used herein,“electrolyte accessible conductive material area” is used to refer tothe total surface area of the conductive material (e.g., carbon) withinthe electrode that can be contacted by electrolyte. For example,electrolyte accessible conductive material area may comprise conductivematerial surface area within the pores of the electrode, conductivematerial surface area on the external surface of the electrode, etc. Insome instances, electrolyte accessible conductive material area is notobstructed by binder or other materials. In addition, in someembodiments, electrolyte accessible conductive material area does notinclude portions of the conductive material that reside within poresthat restrict electrolyte flow due to surface tension effects. In somecases, the electrode comprises an electrolyte accessible conductivematerial area (e.g., an electrolyte accessible carbon area, anelectrolyte accessible metal area) of at least about 1 m², at leastabout 5 m², at least about 10 m², at least about 20 m², at least about50 m², or at least about 100 m² per gram of electrode active material(e.g., sulfur) in the electrode. The relatively large electrolyteaccessible conductive material areas described above can be achieved, insome cases, while an anisotropic force (e.g., defining a pressure ofbetween about 4.9 Newtons/cm² and about 198 Newtons/cm², or any of theranges outlined below) is applied to the electrochemical cell.

Although the electrodes described herein can find use in a wide varietyof electrochemical devices, an example of one such device is provided inFIG. 1 for illustrative purposes only. A general embodiment of anelectrochemical cell can include a cathode, an anode, and an electrolytelayer in electrochemical communication with the cathode and the anode.In some cases, the cell also may comprise a containment structure. Thecomponents may be assembled, in some cases, such that the electrolyte isplaced between the cathode and anode in a stacked configuration. FIG. 1illustrates an electrochemical cell of the invention. In the embodimentshown, cell 10 includes a cathode 30 that can be formed on asubstantially planar surface of substrate 20. While the cathode andsubstrate in FIG. 1 are shown as having a planar configuration, otherembodiments may include non-planar configurations, as will be discussedin more detail later. As noted above, the cathode and/or anode caninclude a porous support structure within which electrode activematerial is contained. For example, in a lithium-sulfur battery, thecathode can comprise a porous support structure within which aelectroactive sulfur-containing material is contained.

The cathode may comprise a variety of cathode active materials. Forexample, the cathode may comprise a sulfur-containing material, whereinsulfur is the cathode active material. Other examples of cathode activematerials are described more fully below. In some embodiments, cathode30 comprises at least one active surface (e.g., surface 32). As usedherein, the term “active surface” is used to describe a surface of anelectrode that is in physical contact with the electrolyte and at whichelectrochemical reactions may take place.

An electrolyte 40 (e.g., comprising a porous separator material) can beformed adjacent the cathode 30. In some embodiments, electrolyte 40 maycomprise a non-solid electrolyte, which may or may not be incorporatedwith a porous separator. As used herein, the term “non-solid” is used torefer to materials that are unable to withstand a static shear stress,and when a shear stress is applied, the non-solid experiences acontinuing and permanent distortion. Examples of non-solids include, forexample, liquids, deformable gels, and the like.

Electrochemical cells described herein may make use of a relatively lowmass of electrolyte relative to the mass of the cathode active materialor the anode active material, in some embodiments. For example, in someinstances, the ratio of electrolyte to cathode active material (e.g.,sulfur) or anode active material, by mass, within the electrochemicalcell is less than about 6:1, less than about 5:1, less than about 4:1,less than about 3:1, or less than about 2:1.

An anode layer 50 can be formed adjacent electrolyte 40 and may be inelectrical communication with the cathode 30. The anode may comprise avariety of anode active materials. For example, the anode may comprise alithium-containing material, wherein lithium is the anode activematerial. Other examples of anode active materials are described morefully below. In some embodiments, anode 50 comprises at least one activesurface (e.g., surface 52). The anode 50 may also be formed on anelectrolyte layer positioned on cathode 30, for example on electrolyte40. Of course, the orientation of the components can be varied, and itshould be understood that there are other embodiments in which theorientation of the layers is varied such that, for example, the anodelayer or the electrolyte layer is first formed on the substrate.

Optionally, the cell may also include, in some embodiments, containmentstructure 56. In addition, the cell may also, optionally, includeadditional layers (not shown), such as a multi-layer structure thatprotects an electroactive material (e.g., an electrode) from theelectrolyte, may be present, as described in more detail in U.S. patentapplication Ser. No. 11/400,781, filed Apr. 6, 2006, entitled,“Rechargeable Lithium/Water, Lithium/Air Batteries” to Affinito et al.,which is incorporated herein by reference in its entirety. Additionally,non-planar arrangements, arrangements with proportions of materialsdifferent than those shown, and other alternative arrangements areuseful in connection with the present invention. A typicalelectrochemical cell also would include, of course, current collectors,external circuitry, housing structure, and the like. Those of ordinaryskill in the art are well aware of the many arrangements that can beutilized with the general schematic arrangement as shown in the figuresand described herein.

While FIG. 1 illustrates an electrochemical cell arranged in a stackedconfiguration, it is to be understood that any electrochemical cellarrangement can be constructed, employing the principles of the presentinvention, in any configuration. For example, FIG. 2 illustrates across-sectional view of an electrochemical cell arranged as a cylinder.In the embodiment shown in FIG. 2, cell 100 includes an electrode 130,an electrolyte 140, and electrode 150. In some embodiments, electrode130 may comprise an anode while electrode 150 may comprise a cathode,while in other embodiments, their order may be reversed. Optionally, thecell may contain a core 170, which may be solid, hollow, or contain achannel or channels. Cell 100 also includes active surfaces 132 and 152.Optionally, the cell may also include, in some embodiments, containmentstructure 156. As shown in FIG. 2, electrode 130 is formed on core 170,electrolyte 140 is formed on electrode 130, and electrode 150 is formedon electrolyte 140. However, in some embodiments, electrode 130 may beproximate core 170, electrolyte 140 may be proximate electrode 130,and/or electrode 150 may be proximate electrolyte 140, optionallyincluding one or more intervening sections of material betweencomponents. In one set of embodiments, electrode 130 may at leastpartially surround core 170, electrolyte 140 may at least partiallysurround electrode 130, and/or electrode 150 may at least partiallysurround electrolyte 140. As used herein, a first entity is “at leastpartially surrounded” by a second entity if a closed loop can be drawnaround the first entity through only the second entity, and does notimply that the first entity is necessarily completely encapsulated bythe second entity.

In another set of embodiments, illustrated in FIG. 3, theelectrochemical cell is in the shape of a folded stack. The cell 200illustrated in FIG. 3 comprises electrolyte 240 separating anode 230 andcathode 250. The electrochemical cell in FIG. 3 comprises an electrolyteincluding three folded planes parallel to arrow 260. In otherembodiments, electrochemical cells may comprise electrolytes includingany number of folded planes parallel to arrow 260. Optionally, the cellmay also include, in some embodiments, containment structure 256. Inaddition to the shapes illustrated in FIGS. 1-3, the electrochemicalcells described herein may be of any other shape including, but notlimited to, prisms (e.g., triangular prisms, rectangular prisms, etc.),“Swiss-rolls,” non-planar stacks, etc. Additional configurations aredescribed in U.S. patent application Ser. No. 11/400,025, filed Apr. 6,2006, entitled, “Electrode Protection in both Aqueous and Non-AqueousElectrochemical Cells, including Rechargeable Lithium Batteries,” toAffinito et al., which is incorporated herein by reference in itsentirety.

Electrochemical cells using the electrodes described herein may becapable of achieving enhanced performance. In some embodiments, theelectrochemical cell may exhibit high electrode active speciesutilization. As used herein, “utilization” refers to the extent to whichthe electrode active material (e.g., sulfur as the cathode activematerial) within a cell reacts to form desirable reaction products, suchthat the electrochemical performance (as measured by the dischargecapacity) is enhanced. For example, an electrochemical cell is said toutilize 100% of the total sulfur in the cell when all of the sulfur inthe cell is completely converted to the desired reaction product (e.g.,S²⁻ in the case of sulfur as the active cathode material), thusproviding the theoretical discharge capacity of 1672 mAh/g of totalsulfur in the cell. It is to be understood that wherever “sulfur” isused as an exemplary electrode active material (e.g., cathode activematerial), any other electrode active material suitable for use with theinvention can be substituted. The theoretical capacity of any electrodeactive material can be calculated by the following formula:

$Q = \frac{nF}{3600\mspace{14mu} M}$

wherein,

Q=Theoretical capacity, Ah/g (ampere hour per gram)

n=number of electrons involved in the desired electrochemical reaction,

F=Faraday constant, 96485 C/equi,

M=Molecular mass of electrode active material, gram

3600=Number of seconds in one hour.

Those of ordinary skill in the art would be able to calculate the activematerial theoretical capacity and compare it to the experimental activematerial capacity for a particular material to determine whether or notthe experimental capacity is at least some percent (e.g., 60%), orgreater, of the theoretical capacity. For example, when elemental sulfur(S) is used as the cathode active material and S²⁻ is the desiredreaction product, the theoretical capacity is 1672 mAh/g. That is, acell is said to utilize 100% of the total sulfur in the cell when itproduces 1672 mAh/g of total sulfur in the cell, 90% of the total sulfurin the cell when it produces 1504.8 mAh/g of total sulfur in the cell,60% of the total sulfur in the cell when it produces 1003.2 mAh/g oftotal sulfur in the cell, and 50% of the total sulfur in the cell whenit produces 836 mAh/g of total sulfur in the cell.

In some embodiments, it is possible for the amount of sulfur (or otheractive material) in the region of the cell that is enclosed by thecathode and anode (“available” sulfur) to be less than that of the totalsulfur in the cell. In some cases the electrolyte may be located both inthe region enclosed by the anode and cathode and the region not enclosedby the cathode and anode. For example, during charge/discharge cyclesunder pressure, it is possible for the un-reacted species in the regionenclosed by anode and cathode to move out either by diffusion or by themovement of the electrolyte. The utilization expressed based on this“available” electrode active material is the measure of the ability ofthe cathode structure to facilitate the conversion of the electrodeactive material in the region enclosed between the cathode and anode todesirable reaction product (e.g., S²⁻ in the case of sulfur as theactive cathode material). For example, if all the sulfur available inthe region enclosed between the cathode and anode is completelyconverted to desired reaction product, then the cell will be said toutilize 100% of the available sulfur, and will produce 1672 mAh/g ofavailable sulfur.

In some embodiments, the electrochemical cell can be designed in such away that either all of the electrolyte is located in between the regionenclosed by the anode and cathode or the transport of un-reacted speciesfrom the enclosed region to the outside is completely eliminated. Forsuch embodiments, the utilization expressed as mAh/g of available sulfurwill be equal to that expressed as mAh/g of total sulfur in the cell.

Electrode active material (e.g., sulfur) utilization may vary with thedischarge current applied to the cell, among other things. In someembodiments, electrode active material utilization at low dischargerates may be higher than electrode active material utilization at highdischarge rates. In some embodiments, the cell is capable of utilizingat least about 60%, at least about 65%, at least about 70%, at leastabout 75%, at least about 80%, at least about 85%, at least about 90%,or at least about 92% of the total electrode active material (e.g.,sulfur) in the cell over at least one charge and discharge cycle. Insome embodiments, the cell is capable of utilizing at least about 60%,at least about 65%, at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, or at least about 92%of the available electrode active material (e.g., sulfur) over at leastone charge and discharge cycle.

In some cases, the utilization rates of electrochemical cells describedherein may remain relatively high through a relatively large number ofcharge and discharge cycles. As used herein, a “charge and dischargecycle” refers to the process by which a cell is charged from 0% to 100%state of charge (SOC) and discharged from 100% back to 0% SOC. In someembodiments, the electrochemical cell may be capable of utilizing atleast about 60%, at least about 65%, at least about 70%, at least about75%, at least about 80%, at least about 85%, or at least about 90% ofthe sulfur (e.g., total sulfur in the cell, available sulfur) or otherelectrode active material through at least a first charge and dischargecycle and at least about 1, 2, 10, 20, 30, 50, 75, 100, 125, or 135charge and discharge cycles subsequent to the first charge and dischargecycle. In certain embodiments, electrochemical cells of the presentinvention will cycle at least 1 time, at least 2 times, at least 10times, at least 20 times, at least 30 times, at least 50 times, at least75 times, at least 100 times, at least 125 times, or at least 135 timessubsequent to a first charge and discharge cycle with each cycle havinga sulfur utilization (measured as a fraction of 1672 mAh/g sulfur (e.g.,total sulfur in the cell, available sulfur) output during the dischargephase of the cycle) or other electrode active material utilization of atleast about 40-50%, at least about 50-60%, at least about 40-60%, atleast about 40-80%, at least about 60-70%, at least about 70%, at leastabout 70-80%, at least about 80%, at least about 80-90%, or at leastabout 90% when discharged at a moderately high discharge current of atleast about 100 mA/g of sulfur (e.g., a discharge current between100-200 mA/g, between 200-300 mA/g, between 300-400 mA/g, between400-500 mA/g, or between 100-500 mA/g).

Some of the electrochemical cells described herein may maintain capacityover a relatively large number of charge and discharge cycles. Forexample, in some cases, the electrochemical cell capacity decreases byless than about 0.2% per charge and discharge cycle over at least about2, at least about 10, at least about 20, at least about 30, at leastabout 50, at least about 75, at least about 100, at least about 125, orat least about 135 cycles subsequent to a first charge and dischargecycle.

In some embodiments, the electrochemical cells described herein mayexhibit relatively high capacities after repeated cycling of the cell.For example, in some embodiments, after alternatively discharging andcharging the cell three times, the cell exhibits at least about 50%, atleast about 80%, at least about 90%, or at least about 95% of the cell'sinitial capacity at the end of the third cycle. In some cases, afteralternatively discharging and charging the cell ten times, the cellexhibits at least about 50%, at least about 80%, at least about 90%, orat least about 95% of the cell's initial capacity at the end of thetenth cycle. In still further cases, after alternatively discharging andcharging the cell twenty-five times, the cell exhibits at least about50%, at least about 80%, at least about 90%, or at least about 95% ofthe cell's initial capacity at the end of the twenty-fifth cycle.

In some embodiments, the electrochemical cells described herein mayachieve relatively high charge efficiencies over a large number ofcycles. As used herein, the “charge efficiency” of the Nth cycle iscalculated as the discharge capacity of the (N+1)th cycle divided by thecharge capacity of the Nth cycle (where N is an integer), and isexpressed as a percentage. In some cases, electrochemical cells mayachieve charge efficiencies of at least about 60%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, at leastabout 97%, at least about 98%, at least about 99%, at least about 99.5%,or at least about 99.9% for the first cycle. In some embodiments, chargeefficiencies of at least about 60%, at least about 70%, at least about80%, at least about 90%, at least about 97%, at least about 98%, atleast about 99%, at least about 99.5%, or at least about 99.9% may beachieved for the 10th, 20th, 30th, 50th, 75th, 100^(th), 125th, or 135thcycles subsequent to a first charge and discharge cycle.

The electrochemical cells described herein may be operated usingrelatively high discharge current densities, in some cases. As usedherein, the “discharge current density” refers to the discharge currentbetween the electrodes, divided by the area of the electrode over whichthe discharge occurs, as measured perpendicular to the direction of thecurrent. For the purposes of discharge current density, the area of theelectrode does not include the total exposed surface area of theelectrode, but rather, refers to an imaginary plane drawn along theelectrode surface perpendicular to the direction of the current. In someembodiments, the electrochemical cells may be operated at a dischargecurrent density of at least about 0.1 mA/cm², at least about 0.2 mA/cm²,at least about 0.4 mA/cm² of the cathode surface, or higher. The cellsdescribed herein may also be operated, in some cases, at a highdischarge current per unit mass of active material. For example, thedischarge current may be at least about 100, at least about 200, atleast about 300, at least about 400, or at least about 500 mA per gramof active material in an electrode (e.g., sulfur in the cathode), orhigher.

Some embodiments may include electrochemical devices in which theapplication of force is used to enhance the performance of the device.For example, the force may provide improved electrical conductivitybetween conductive material in an electrode (e.g., carbon in a cathode).In some instances, the application of force to the electrochemical cellmay reduce the amount of roughening of one or more surfaces of one ormore electrodes which may improve the cycling lifetime and performanceof the cell. Any of the electrode properties (e.g., porosities, poresize distributions, etc.) and/or performance metrics outlined above maybe achieved, alone or in combination with each other, while ananisotropic force is applied to the electrochemical cell (e.g., duringcharge and/or discharge of the cell). The magnitude of the anisotropicforce may lie within any of the ranges mentioned below.

In some embodiments, the application of force can be used to enhance theperformance of the device. In some embodiments, the force comprises ananisotropic force with a component normal to the active surface of theanode. In the case of a planar surface, the force may comprise ananisotropic force with a component normal to the surface at the point atwhich the force is applied. For example, referring to FIG. 1, a forcemay be applied in the direction of arrow 60. Arrow 62 illustrates thecomponent of the force that is normal to active surface 52 of anode 50.In the case of a curved surface, for example, a concave surface or aconvex surface, the force may comprise an anisotropic force with acomponent normal to a plane that is tangent to the curved surface at thepoint at which the force is applied. Referring to the cylindrical cellillustrated in FIG. 2, a force may be applied to an external surface ofthe cell in the direction of, for example, arrow 180. In someembodiments, the force may be applied from the interior of thecylindrical cell, for example, in the direction of arrow 182. In someembodiments, an anisotropic force with a component normal to the activesurface of the anode is applied during at least one period of timeduring charge and/or discharge of the electrochemical cell. In someembodiments, the force may be applied continuously, over one period oftime, or over multiple periods of time that may vary in duration and/orfrequency. The anisotropic force may be applied, in some cases, at oneor more pre-determined locations, optionally distributed over the activesurface of the anode. In some embodiments, the anisotropic force isapplied uniformly over the active surface of the anode.

An “anisotropic force” is given its ordinary meaning in the art andmeans a force that is not equal in all directions. A force equal in alldirections is, for example, internal pressure of a fluid or materialwithin the fluid or material, such as internal gas pressure of anobject. Examples of forces not equal in all directions include forcesdirected in a particular direction, such as the force on a table appliedby an object on the table via gravity. Another example of an anisotropicforce includes a force applied by a band arranged around a perimeter ofan object. For example, a rubber band or turnbuckle can apply forcesaround a perimeter of an object around which it is wrapped. However, theband may not apply any direct force on any part of the exterior surfaceof the object not in contact with the band. In addition, when the bandis expanded along a first axis to a greater extent than a second axis,the band can apply a larger force in the direction parallel to the firstaxis than the force applied parallel to the second axis.

A force with a “component normal” to a surface, for example an activesurface of an anode, is given its ordinary meaning as would beunderstood by those of ordinary skill in the art and includes, forexample, a force which at least in part exerts itself in a directionsubstantially perpendicular to the surface. For example, in the case ofa horizontal table with an object resting on the table and affected onlyby gravity, the object exerts a force essentially completely normal tothe surface of the table. If the object is also urged laterally acrossthe horizontal table surface, then it exerts a force on the table which,while not completely perpendicular to the horizontal surface, includes acomponent normal to the table surface. Those of ordinary skill canunderstand other examples of these terms, especially as applied withinthe description of this document.

In some embodiments, the anisotropic force can be applied such that themagnitude of the force is substantially equal in all directions within aplane defining a cross-section of the electrochemical cell, but themagnitude of the forces in out-of-plane directions is substantiallyunequal to the magnitudes of the in-plane forces. For example, referringto FIG. 2, a cylindrical band may be positioned around the exterior ofcell 100 such that forces (e.g., force 180) are applied to the celloriented toward the cell's central axis (indicated by point 190 andextending into and out of the surface of the cross-sectional schematicdiagram). In some embodiments, the magnitudes of the forces orientedtoward the central axis of the cell are different (e.g., greater than)the magnitudes of the forces applied in out of plane directions (e.g.,parallel to central axis 190).

In one set of embodiments, cells of the invention are constructed andarranged to apply, during at least one period of time during chargeand/or discharge of the cell, an anisotropic force with a componentnormal to the active surface of the anode. Those of ordinary skill inthe art will understand the meaning of this. In such an arrangement, thecell may be formed as part of a container which applies such a force byvirtue of a “load” applied during or after assembly of the cell, orapplied during use of the cell as a result of expansion and/orcontraction of one or more portions of the cell itself.

The magnitude of the applied force is, in some embodiments, large enoughto enhance the performance of the electrochemical cell. The anode activesurface and the anisotropic force may be, in some instances, togetherselected such that the anisotropic force affects surface morphology ofthe anode active surface to inhibit increase in anode active surfacearea through charge and discharge and wherein, in the absence of theanisotropic force but under otherwise essentially identical conditions,the anode active surface area is increased to a greater extent throughcharge and discharge cycles. “Essentially identical conditions,” in thiscontext, means conditions that are similar or identical other than theapplication and/or magnitude of the force. For example, otherwiseidentical conditions may mean a cell that is identical, but where it isnot constructed (e.g., by brackets or other connections) to apply theanisotropic force on the subject cell.

Electrode materials or structures and anisotropic forces can be selectedtogether, to achieve results described herein, by those of ordinaryskill in the art. For example, where the electrode(s) is relativelysoft, the component of the force normal to the active anode surface maybe selected to be lower. Where the electrode(s) is harder, the componentof the force normal to the active surface may be greater. Those ofordinary skill in the art can easily select electrode materials, alloys,mixtures, etc. with known or predictable properties, or readily test thehardness or softness of such surfaces, and readily select cellconstruction techniques and arrangements to provide appropriate forcesto achieve what is described herein. Simple testing can be done, forexample by arranging a series of active materials, each with a series offorces applied normal (or with a component normal) to the activesurface, to determine the morphological effect of the force on thesurface without cell cycling (for prediction of the selected combinationduring cell cycling) or with cell cycling with observation of a resultrelevant to the selection.

In some embodiments, an anisotropic force with a component normal to theactive surface of the anode is applied, during at least one period oftime during charge and/or discharge of the cell, to an extent effectiveto inhibit an increase in surface area of the anode active surfacerelative to an increase in surface area absent the anisotropic force.The component of the anisotropic force normal to the anode activesurface may, for example, define a pressure of at least about 4.9, atleast about 9.8, at least about 24.5, at least about 49, at least about78, at least about 98, at least about 117.6, at least about 147, atleast about 175, at least about 200, at least about 225, or at leastabout 250 Newtons per square centimeter. In some embodiments, thecomponent of the anisotropic force normal to the anode active surfacemay, for example, define a pressure of less than about 250, less thanabout 225, less than about 196, less than about 147, less than about117.6, less than about 98, less than about 49, less than about 24.5, orless than about 9.8 Newtons per square centimeter. In some cases, thecomponent of the anisotropic force normal to the anode active surface ismay define a pressure of between about 4.9 and about 147 Newtons persquare centimeter, between about 49 and about 117.6 Newtons per squarecentimeter, between about 68.6 and about 98 Newtons per squarecentimeter, between about 78 and about 108 Newtons per squarecentimeter, between about 4.9 and about 250 Newtons per squarecentimeter, between about 49 and about 250 Newtons per squarecentimeter, between about 80 and about 250 Newtons per squarecentimeter, between about 90 and about 250 Newtons per squarecentimeter, or between about 100 and about 250 Newtons per squarecentimeter. While forces and pressures are generally described herein inunits of Newtons and Newtons per unit area, respectively, forces andpressures can also be expressed in units of kilograms-force andkilograms-force per unit area, respectively. One of ordinary skill inthe art will be familiar with kilogram-force-based units, and willunderstand that 1 kilogram-force (kg_(f)) is equivalent to about 9.8Newtons.

In some embodiments, the surface of an electrode layer can be enhancedduring cycling (e.g., for lithium, the development of mossy or a roughsurface of lithium may be reduced or eliminated) by application of anexternally-applied (in some embodiments, uniaxial) pressure. Theexternally-applied pressure may, in some embodiments, be chosen to begreater than the yield stress of a material forming the electrodematerial layer. For example, for an electrode material comprisinglithium, the cell may be under an externally-applied anisotropic forcewith a component defining a pressure of at least about 8 kg_(f)/cm², atleast about 9 kg_(f)/cm², or at least about 10 kg_(f)/cm². This isbecause the yield stress of lithium is around 7-8 kg_(f)/cm². Thus, atpressures (e.g., uniaxial pressures) greater than this value, mossy Li,or any surface roughness at all, may be reduced or suppressed. Thelithium surface roughness may mimic the surface that is pressing againstit. Accordingly, when cycling under at least about 8 kg_(f)/cm², atleast about 9 kg_(f)/cm², or at least about 10 kg_(f)/cm² ofexternally-applied pressure, the lithium surface may become smootherwith cycling when the pressing surface is smooth. As described herein,the pressing surface may be modified by choosing the appropriatematerial(s) positioned between the anode and the cathode. For instance,in some cases the smoothness of the lithium surface (or surface of otheractive electrode materials) can be increased, during application ofpressure, by the use of an electrically non-conductive material layer asdescribed herein.

In some cases, one or more forces applied to the cell have a componentthat is not normal to an active surface of an anode. For example, inFIG. 1, force 60 is not normal to anode active surface 52, and force 60includes component 64, which is substantially parallel to anode activesurface 52. In addition, a force 66, which is substantially parallel toanode active surface 52, could be applied to the cell in some cases. Inone set of embodiments, the sum of the components of all appliedanisotropic forces in a direction normal to the anode active surface islarger than any sum of components in a direction that is non-normal tothe anode active surface. In some embodiments, the sum of the componentsof all applied anisotropic forces in a direction normal to the anodeactive surface is at least about 5%, at least about 10%, at least about20%, at least about 35%, at least about 50%, at least about 75%, atleast about 90%, at least about 95%, at least about 99%, or at leastabout 99.9% larger than any sum of components in a direction that isparallel to the anode active surface.

In some embodiments, the cathode and anode have yield stresses, whereinthe effective yield stress of one of the cathode and anode is greaterthan the yield stress of the other, such that an anisotropic forceapplied normal to the surface of one of the active surface of the anodeand the active surface of the cathode causes the surface morphology ofone of the cathode and the anode to be affected. In some embodiments,the component of the anisotropic force normal to the active anodesurface is between about 20% and about 200% of the yield stress of theanode material, between about 50% and about 120% of the yield stress ofthe anode material, between about 80% and about 120% of the yield stressof the anode material, between about 80% and about 100% of the yieldstress of the anode material, between about 100% and about 300% of theyield stress of the anode material, between about 100% and about 200% ofthe yield stress of the anode material, or between about 100% and about120% of the yield stress of the anode material.

The anisotropic force described herein may be applied using any methodknown in the art. In some embodiments, the force may be applied usingcompression springs. Forces may be applied using other elements (eitherinside or outside a containment structure) including, but not limited toBelleville washers, machine screws, pneumatic devices, and/or weights,among others. In some cases, cells may be pre-compressed before they areinserted into containment structures, and, upon being inserted to thecontainment structure, they may expand to produce a net force on thecell. Suitable methods for applying such forces are described in detail,for example, in U.S. Provisional Application No. 61/086,329, filed Aug.5, 2008, entitled “Application of Force in Electrochemical Cells” toScordilis-Kelley et al., and U.S. patent application Ser. No.12/535,328, filed Aug. 4, 2009, entitled “Application of Force inElectrochemical Cells” to Scordilis-Kelley et al. which are incorporatedherein by reference in their entirety.

In some embodiments, the application of a force as described herein mayallow for the use of smaller amounts of anode active material (e.g.,lithium) and/or electrolyte within an electrochemical cell, relative tothe amounts used in essentially identical cells in which the force isnot applied. In cells lacking the applied force described herein, activeanode material (e.g., lithium metal) may be, in some cases, redepositedunevenly on an anode during charge-discharge cycles of the cell, forminga rough surface. In some cases, this may lead to an increase in therates of one or more undesired reactions involving the anode metal.These undesired reactions may, after a number of charge-dischargecycles, stabilize and/or begin to self-inhibit such that substantiallyno additional active anode material becomes depleted and the cell mayfunction with the remaining active materials. For cells lacking theapplied force as described herein, this “stabilization” is often reachedonly after a substantial amount of anode active material has beenconsumed and cell performance has deteriorated. Therefore, in some caseswhere forces as described herein have not been applied, a relativelylarge amount of anode active material and/or electrolyte has often beenincorporated within cells to accommodate for loss of material duringconsumption of active materials, in order to preserve cell performance.

Accordingly, the application of force as described herein may reduceand/or prevent depletion of active materials such that the inclusion oflarge amounts of anode active material and/or electrolyte within theelectrochemical cell may not be necessary. For example, the force may beapplied to a cell prior to use of the cell, or in an early stage in thelifetime of the cell (e.g., less than five charge-discharge cycles),such that little or substantially no depletion of active material mayoccur upon charging or discharging of the cell. By reducing and/oreliminating the need to accommodate for active material loss duringcharge-discharge of the cell, relatively small amounts of anode activematerial may be used to fabricate cells and devices as described herein.In some embodiments, the invention relates to devices comprising anelectrochemical cell having been charged and discharged less than fivetimes in its lifetime, wherein the cell comprises an anode, a cathode,and an electrolyte, wherein the anode comprises no more than five timesthe amount of anode active material which can be ionized during one fulldischarge cycle of the cell. In some cases, the anode comprises no morethan four, three, two, or 1.5 times the amount of lithium which can beionized during one full discharge cycle of the cell.

In some cases, the devices described herein can comprise anelectrochemical cell, wherein the cell comprises an anode activematerial, a cathode active material, and an electrolyte, wherein theratio of the amount of anode active material in the anode to the amountof cathode active material in the cathode is less than about 5:1, lessthan about 3:1, less than about 2:1, or less than about 1.5:1 on a molarbasis. For example, a cell may comprise lithium as an active anodematerial and sulfur as an active cathode material, wherein the molarratio Li:S is less than about 5:1. In some cases, the molar ratio oflithium to sulfur, Li:S, is less than about 3:1, less than about 2:1, orless than about 1.5:1. In some embodiments, the ratio of anode activematerial (e.g., lithium) to cathode active material by weight may beless than about 2:1, less than about 1.5:1, less than about 1.25:1, orless than about 1.1:1. For example, a cell may comprise lithium as theactive anode material and sulfur as the active cathode material, whereinthe ratio Li:S by weight is less than about 2:1, less than about 1.5:1,less than about 1.25:1, or less than about 1.1:1.

The use of smaller amounts of active anode material and/or electrolytematerial may advantageously allow for electrochemical cells, or portionsthereof, having decreased thickness. In some embodiments, the anodelayer and the electrolyte layer together have a maximum thickness ofabout 500 microns. In some cases, the anode layer and the electrolytelayer together have a maximum thickness of about 400 microns, about 300microns, about 200 microns, about 100 microns, about 50 microns, or, insome cases, about 20 microns.

The anodes described herein may include a variety of electroactivematerials. Suitable electroactive materials for use as anode activematerials in the anode of the electrochemical cells described hereininclude, but are not limited to, lithium metal such as lithium foil andlithium deposited onto a conductive substrate, and lithium alloys (e.g.,lithium-aluminum alloys and lithium-tin alloys). While these arepreferred negative electrode materials, the current collectors may alsobe used with other cell chemistries. In some embodiments, the anode maycomprise one or more binder materials (e.g., polymers, etc.).

In some embodiments, an electroactive lithium-containing material of ananode active layer comprises greater than 50 wt % lithium. In somecases, the electroactive lithium-containing material of an anode activelayer comprises greater than 75 wt % lithium. In still otherembodiments, the electroactive lithium-containing material of an anodeactive layer comprises greater than 90 wt % lithium.

Positive and/or negative electrodes may optionally include one or morelayers that interact favorably with a suitable electrolyte, such asthose described in U.S. patent application Ser. No. 12/312,764, filedMay 26, 2009 and entitled “Separation of Electrolytes,” by Mikhaylik etal., which is incorporated herein by reference in its entirety.

The electrolytes used in electrochemical or battery cells can functionas a medium for the storage and transport of ions, and in the specialcase of solid electrolytes and gel electrolytes, these materials mayadditionally function as a separator between the anode and the cathode.Any liquid, solid, or gel material capable of storing and transportingions may be used, so long as the material facilitates the transport ofions (e.g., lithium ions) between the anode and the cathode. Theelectrolyte is electronically non-conductive to prevent short circuitingbetween the anode and the cathode. In some embodiments, the electrolytemay comprise a non-solid electrolyte.

In some embodiments, the electrolyte comprises a fluid that can be addedat any point in the fabrication process. In some cases, theelectrochemical cell may be fabricated by providing a cathode and ananode, applying an anisotropic force component normal to the activesurface of the anode, and subsequently adding the fluid electrolyte suchthat the electrolyte is in electrochemical communication with thecathode and the anode. In other cases, the fluid electrolyte may beadded to the electrochemical cell prior to or simultaneously with theapplication of the anisotropic force component, after which theelectrolyte is in electrochemical communication with the cathode and theanode.

The electrolyte can comprise one or more ionic electrolyte salts toprovide ionic conductivity and one or more liquid electrolyte solvents,gel polymer materials, or polymer materials. Suitable non-aqueouselectrolytes may include organic electrolytes comprising one or morematerials selected from the group consisting of liquid electrolytes, gelpolymer electrolytes, and solid polymer electrolytes. Examples ofnon-aqueous electrolytes for lithium batteries are described by Dornineyin Lithium Batteries, New Materials, Developments and Perspectives,Chapter 4, pp. 137-165, Elsevier, Amsterdam (1994). Examples of gelpolymer electrolytes and solid polymer electrolytes are described byAlamgir et al. in Lithium Batteries, New Materials, Developments andPerspectives, Chapter 3, pp. 93-136, Elsevier, Amsterdam (1994).Heterogeneous electrolyte compositions that can be used in batteriesdescribed herein are described in U.S. patent application Ser. No.12/312,764, filed May 26, 2009 and entitled “Separation ofElectrolytes,” by Mikhaylik et al., which is incorporated herein byreference in its entirety.

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, aliphatic ethers, cyclic ethers, glymes,polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Fluorinated derivatives of the foregoing are also useful asliquid electrolyte solvents.

In some cases, aqueous solvents can be used as electrolytes, forexample, in lithium cells. Aqueous solvents can include water, which cancontain other components such as ionic salts. As noted above, in someembodiments, the electrolyte can include species such as lithiumhydroxide, or other species rendering the electrolyte basic, so as toreduce the concentration of hydrogen ions in the electrolyte.

Liquid electrolyte solvents can also be useful as plasticizers for gelpolymer electrolytes, i.e., electrolytes comprising one or more polymersforming a semi-solid network. Examples of useful gel polymerelectrolytes include, but are not limited to, those comprising one ormore polymers selected from the group consisting of polyethylene oxides,polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides,polyphosphazenes, polyethers, sulfonated polyimides, perfluorinatedmembranes (NAFION resins), polydivinyl polyethylene glycols,polyethylene glycol diacrylates, polyethylene glycol dimethacrylates,polysulfones, polyethersulfones, derivatives of the foregoing,copolymers of the foregoing, crosslinked and network structures of theforegoing, and blends of the foregoing, and optionally, one or moreplasticizers. In some embodiments, a gel polymer electrolyte comprisesbetween 10-20%, 20-40%, between 60-70%, between 70-80%, between 80-90%,or between 90-95% of a heterogeneous electrolyte by volume.

In some embodiments, one or more solid polymers can be used to form anelectrolyte. Examples of useful solid polymer electrolytes include, butare not limited to, those comprising one or more polymers selected fromthe group consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming electrolytes, the electrolyte may furthercomprise one or more ionic electrolyte salts, also as known in the art,to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytes of thepresent invention include, but are not limited to, LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂. Other electrolyte salts that may beuseful include lithium polysulfides (Li₂S_(x)), and lithium salts oforganic polysulfides (LiS_(x)R)_(n), where x is an integer from 1 to 20,n is an integer from 1 to 3, and R is an organic group, and thosedisclosed in U.S. Pat. No. 5,538,812 to Lee et al.

In some embodiments, electrochemical cells may further comprise aseparator interposed between the cathode and anode. The separator may bea solid non-conductive or insulative material which separates orinsulates the anode and the cathode from each other preventing shortcircuiting, and which permits the transport of ions between the anodeand the cathode. In some embodiments, the porous separator may bepermeable to the electrolyte.

The pores of the separator may be partially or substantially filled withelectrolyte. Separators may be supplied as porous free standing filmswhich are interleaved with the anodes and the cathodes during thefabrication of cells. Alternatively, the porous separator layer may beapplied directly to the surface of one of the electrodes, for example,as described in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley et al.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes (e.g., SETELA™ madeby Tonen Chemical Corp) and polypropylenes, glass fiber filter papers,and ceramic materials. For example, in some embodiments, the separatorcomprises a microporous polyethylene film. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree standing film or by a direct coating application on one of theelectrodes, as described in U.S. Pat. Nos. 6,153,337 and 6,306,545 byCarlson et al. of the common assignee. Solid electrolytes and gelelectrolytes may also function as a separator in addition to theirelectrolyte function.

The following documents are incorporated herein by reference in theirentireties for all purposes: U.S. Provisional Patent Application No.61/237,903, filed Aug. 28, 2009, and entitled “Electrochemical CellsComprising Porous Structures Comprising Sulfur;” U.S. Pat. No.7,247,408, filed May 23, 2001, entitled “Lithium Anodes forElectrochemical Cells”; U.S. Pat. No. 5,648,187, filed Mar. 19, 1996,entitled “Stabilized Anode for Lithium-Polymer Batteries”; U.S. Pat. No.5,961,672, filed Jul. 7, 1997, entitled “Stabilized Anode forLithium-Polymer Batteries”; U.S. Pat. No. 5,919,587, filed May 21, 1997,entitled “Novel Composite Cathodes, Electrochemical Cells ComprisingNovel Composite Cathodes, and Processes for Fabricating Same”; U.S.patent application Ser. No. 11/400,781, filed Apr. 6, 2006, entitled“Rechargeable Lithium/Water, Lithium/Air Batteries”; InternationalPatent Apl. Serial No.: PCT/US2008/009158, filed Jul. 29, 2008, entitled“Swelling Inhibition in Lithium Batteries”; U.S. patent application Ser.No. 12/312,764, filed May 26, 2009, entitled “Separation ofElectrolytes”; International Patent Apl. Serial No.: PCT/US2008/012042,filed Oct. 23, 2008, entitled “Primer for Battery Electrode”; U.S.patent application Ser. No. 12/069,335, filed Feb. 8, 2008, entitled“Protective Circuit for Energy-Storage Device”; U.S. patent applicationSer. No. 11/400,025, filed Apr. 6, 2006, entitled “Electrode Protectionin both Aqueous and Non-Aqueous Electrochemical Cells, includingRechargeable Lithium Batteries”; U.S. patent application Ser. No.11/821,576, filed Jun. 22, 2007, entitled “Lithium Alloy/SulfurBatteries”; patent application Ser. No. 11/111,262, filed Apr. 20, 2005,entitled “Lithium Sulfur Rechargeable Battery Fuel Gauge Systems andMethods”; U.S. patent application Ser. No. 11/728,197, filed Mar. 23,2007, entitled “Co-Flash Evaporation of Polymerizable Monomers andNon-Polymerizable Carrier Solvent/Salt Mixtures/Solutions”;International Patent Apl. Serial No.: PCT/US2008/010894, filed Sep. 19,2008, entitled “Electrolyte Additives for Lithium Batteries and RelatedMethods”; International Patent Apl. Serial No.: PCT/US2009/000090, filedJan. 8, 2009, entitled “Porous Electrodes and Associated Methods”; U.S.patent application Ser. No. 12/535,328, filed Aug. 4, 2009, entitled“Application of Force In Electrochemical Cells”; U.S. patent applicationSer. No. 12/727,862, filed Mar. 19, 2010, entitled “Cathode for LithiumBattery”; U.S. patent application Ser. No. 12,471,095, filed May 22,2009, entitled “Hermetic Sample Holder and Method for PerformingMicroanalysis Under Controlled Atmosphere Environment”; a U.S. PatentApplication, filed on even date herewith, entitled “Release System forElectrochemical cells (which claims priority to Provisional Patent Apl.Ser. No. 61/236,322, filed Aug. 24, 2009, entitled “Release System forElectrochemical Cells”); a U.S. Provisional Application, filed on evendate herewith, entitled “Separator for Electrochemical Cell;” a U.S.Patent Application, filed on even date herewith, entitled“Electrochemical Cell;” and 3 U.S. Patent Applications, filed on evendate herewith, entitled “Electrochemical Cells Comprising PorousStructures Comprising Sulfur.”

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

Example 1

This example describes the fabrication and testing of a cathodecomprising a porous support structure in which particles comprisingsulfur were deposited. 100 grams of elemental sulfur (available fromAldrich Chemical Company, Milwaukee, Wis.), were dissolved in 1200 mL oftoluene (Aldrich) at 103° C. in a round bottom flask fitted with acondenser. 100 grams of Printex® XE-2 (a carbon pigment available fromDegussa Corporation, Akron, Ohio) conductive carbon (surface area800-1000 m²/g, absorption stiffness 350-410 mL dibutyl phthalate(DBP)/100 g XE-2), was added to the solution. The solution was quicklyabsorbed by the carbon. After a couple of hours of stiffing, the mixturewas cooled to room temperature, where sulfur has lower solubility intoluene (84 mM). After cooling, the sulfur crystallized in the carbonpores, and the excess toluene was filtered off.

The sulfur-filled carbon material was dried and mixed with appropriateamounts of polyvinyl alcohol binder (Celvol 425 from CelaneseCorporation) dissolved in a 1:1 weight ratio mixture of isopropanol andwater. The cathode slurry was coated onto a conductive carbon coatedAluminum foil substrate (7-μm-thick from All Foils). After drying, thecoated cathode active layer thickness was about 110 microns. Theresultant cathode was easy to coat, included a homogeneous distributionof small particle size sulfur, and had uniform porosity, as shown inFIG. 4A.

An electrochemical cell including the cathode was assembled for testing.Lithium metal (>99.9% Li, 2 mil thick foil from Chemetall-Foote Corp.,Kings Mountain, N.C.) was used for the anode. The electrolyte included 8parts of lithium bis (trifluoromethane sulfonyl) imide, (lithium imideavailable from 3M Corporation, St. Paul, Minn.), 3.8 parts lithiumnitrate (available from Aldrich Chemical Company, Milwaukee, Wis.), 1part guanidine nitrate (also available from Aldrich Chemical Company,Milwaukee, Wis.) and 0.4 parts pyridine nitrate (synthesized in-housefrom pyridine and nitric acid) in a 1:1 weight ratio mixture of1,3-dioxolane and dimethoxyethane. The electrolyte included a watercontent of less than 50 ppm. A porous separator comprising 9-1 μm SETELA(a polyolefin separator available from Tonen Chemical Corporation,Tokyo, Japan, and from Mobil Chemical Company, Films Division,Pittsford, N.Y.) was included between the anode and the cathode. Theanode, cathode, separator, and electrolyte were stacked into a layeredstructure of 6×(cathode/separator/anode), which was compressed betweentwo parallel plates at a pressure of 196 Newtons/cm² (about 20kg-force/cm²). The liquid electrolyte filled the void areas of theseparator and cathode to form prismatic cells with an electrode area ofabout 100 cm². After sealing, the cells were stored for 24 hours.Charge-discharge cycling was performed at 40 mA and 25 mA, respectively.The discharge cutoff voltage was 1.7V and the charge cutoff voltage was2.5V. FIG. 5A includes a plot of specific discharge capacity for thecomposite electrodes (indicated with asterisks) as a function of thenumber of cycles. FIG. 5B includes a plot of the capacity of the cells(indicated with asterisks), expressed as a percentage relative to theinitial maximum, as a function of C-rate. The specific dischargecapacities remained relatively high over multiple cycles. In addition,the cells maintained relatively high capacities at relatively highC-rates.

Comparative Example 1

This example describes the fabrication and testing of a cathodecomprising a mechanical mixture of sulfur and carbon. The first attemptincluded a 1:1 carbon-to-sulfur ratio in the mixture. However, the 1:1mixture could not be effectively deposited on the coater. In subsequentexperiments, the cathode was prepared by preparing a mixture comprising55 parts of elemental sulfur (Aldrich Chemical Company, Milwaukee,Wis.), 40 parts of a conductive carbon pigment Printex® XE-2, and 5parts of polyvinyl alcohol binder. The mixture was dissolved in a 1:1weight ratio mixture of isopropanol and water. The solution was coatedonto a 7-micron-thick conductive carbon coated Aluminum foil substrate.After drying, the coated cathode active layer thickness was about 90microns. The resultant cathode was very heterogeneous with large Sulfurparticles and carbon agglomerates, as shown in FIG. 4B.

An electrochemical cell including the cathode was assembled for testingaccording to the process described in Example 1. FIG. 5A includes a plotof specific discharge capacity of cells comprising mechanically mixedcathodes (indicated with diamonds) as a function of the number ofcycles. FIG. 5B includes a plot of the capacity of cells comprisingmechanically mixed cathodes (indicated with diamonds), expressed as apercentage relative to the initial maximum, as a function of C-rate. Thespecific discharge capacities for cells comprising the mechanicallymixed cathodes were relatively low over the number of tested cycles. Inaddition, the cells comprising mechanically mixed cathodes exhibitedmuch larger decreases in capacity at higher C-rates.

Example 2

This example describes the use of a thermal processing scheme to depositsulfur in porous support materials comprising conductive carbons. Thefollowing conductive carbons were tested: Printex® XE-2, Vulcan XC72R(Cabot Corporation, Tampa, Tex.) and SAB (Shawinigan Acetylene Black,formerly available from Chevron Phillips, The Woodlands, Tex.). Theconductive carbons were heated in an evacuated round bottom flask at300-450° C. for 5 to 6 hours prior to mixing with sulfur. Sulfur powder(Alfa Aesar Corporation, Ward Hill, Mass.) and conductive carbon weremixed together under an inert Ar atmosphere.

The mixture was heated past the meting point of sulfur to 160° C. undervacuum for 5 to 6 hours to produce a yellow, low viscosity fluidcomprising S₈. Heating the mixture beyond the melting point of sulfurresulted in depositing liquid sulfur in the pores of the carbonparticles without the use of solvents. The temperature was then raisedto 250 to 300° C. under reduced pressure for 4 to 6 hours to performpolymerization of adsorbed sulfur. In addition, the heating helped inproducing a uniform surface distribution. After the polymerization step,the composites were rapidly cooled to form composites comprisingpolymeric sulfur and carbon.

Sulfur-filled carbon composites were fabricated with S:C ratios varyingfrom 6:1 to 1:1, depending on the available pore volume and surface areaof the carbon were fabricated using various types of carbon. FIG. 6Aincludes a secondary electron image of the external surface of asulfur-carbon composite particle. FIGS. 6B-6C include X-ray spectralimages outlining the distributions of (B) sulfur and (C) carbon on theexternal surface of the composite particle shown in FIG. 6A. The imagesin FIGS. 6B-6C indicate that the sulfur and carbon were evenlydistributed across the outside surface of the composite particle. FIG.6D includes a secondary electron image of an internal surface of asulfur-carbon composite particle. FIGS. 6E-6F include X-ray spectralimages outlining the distributions of (E) sulfur and (F) carbon on theinternal surface of the composite particle shown in FIG. 6D. The imagesin FIGS. 6E-6F indicate that the sulfur and carbon were evenlydistributed across the internal surface of the composite particle.

The sulfur-carbon composites were mixed with appropriate amounts ofpolyvinyl alcohol binder or Gelatin B (Sigma-Aldrich Chemical Company,Milwaukee, Wis.) and dissolved in a 1:1 weight ratio mixture ofiso-propanol and water. The cathode slurry was coated onto a conductive,carbon-coated Aluminum foil substrate (7 microns thick) in a similarfashion as described in Example 1.

The resultant composite cathode materials had a relatively high density,uniform porosity, and homogeneous sulfur distribution. The sulfur-carboncomposites contained extended, clean sulfur-carbon interfaces that couldbe useful in promoting structure and conductivity. In addition, thisprocess produced little to no waste, and mechanical milling was notrequired. In addition, the carbons and composites could be easilymodified by various gas or vapor treatments during thermo-vacuumactivation at any processing stage, providing for a flexible means offunctionalization (e.g., via metals, oxide powders, sulfide powders,nanotubes, polymer macromolecules, etc.). The composite cathodes werealso relatively easy to coat, and were relatively stable andcompositionally uniform during cycling.

Electrochemical cells including the cathodes were assembled for testing.Lithium metal (>99.9% Li, 2 mil thick foil) was used as the anode. Theelectrolyte included 8 parts of lithium bis(trifluoromethane sulfonyl)imide, 3.8 parts lithium nitrate, 1 part guanidine nitrate, and 0.4parts pyridine nitrate (synthesized in-house from pyridine and nitricacid) in a 1:1 weight ratio mixture of 1,3-dioxolane anddimethoxyethane. The electrolyte included a water content of less than50 ppm. A 9-micron SETELA porous separator was also used.

The above components were assembled into a layered structure ofcathode/separator/anode, which was folded in half to make a bicell. Thebicell was placed in a foil pouch with approximately 0.4 grams of aliquid electrolyte. After storing for 24 hours, the cells were testedwithout compression. FIG. 7 includes a plot of specific dischargecapacity of cells comprising the composite cathodes (indicated withasterisks) as a function of the number of cycles. The cells comprisingthe composite cathodes exhibited relatively high discharge capacitiesrelative to cells comprising mechanically mixed cathodes.

Comparative Example 2

This example describes the fabrication and testing of a cathodecomprising a mechanical mixture of sulfur and carbon in a 1:1 ratio. Aswas observed in Comparative Example 1, a 1:1 carbon-to-sulfurformulation was extremely difficult to produce on the coater. In thisexample, hand drawn-down coatings were fabricated. The electrodesfabricated by this process exhibited dispersities more than two ordersof magnitude lower compared to those observed in the compositestructures described in Example 2. In addition, the hand drawn-downcoatings were more difficult to coat and exhibited relatively highcompositional instabilities during cycling, relative to the compositesdescribed in Example 2.

FIGS. 8A and 8B include secondary electron images of a pristinecomposite cathode (as described in Example 2) and a mechanically mixedcathode, respectively, each comprising a S:XE2 ratio of 84:16. FIGS.9A-9C include X-ray spectral images outlining the distributions of (A)sulfur, (B) carbon, and (C) aluminum in the composite cathode (Example2). In addition, FIGS. 9D-9F include X-ray spectral images outlining thedistributions of (D) sulfur, (E) carbon, and (F) aluminum in themechanically mixed cathode. The composite cathode includes a relativelyuniform distribution of all three elements, compared to the mechanicallymixed cathode. In addition, the domain structure in the compositecathode described in Example 2 was not developed. The thicknesses of thecracks in the composite cathode were two times smaller than those in themechanically mixed cathode, and the crack density of the compositecathode was significantly lower than that observed in the mechanicallymixed cathode.

An electrochemical cell including the mechanically mixed cathode wasassembled for testing according to the process described in Example 2.FIG. 7 includes a plot of specific discharge capacity of cellscomprising the mechanically mixed cathodes (indicated with squares) as afunction of the number of cycles. The cells comprising the mechanicallymixed cathodes exhibited relatively low discharge capacities relative tocells comprising composite cathodes.

Example 3

This example describes the fabrication and testing of a cathodefabricated using a nickel foam. The cathode was prepared by filling thepores of a nickel foam (Incofoam supplied by Novamet, 450 micron pores,density of 320 g/cm²) with a mixture of 75 parts of elemental sulfur, 20parts of Printex® XE-2, 4 parts of graphite powder (Aldrich ChemicalCompany, Milwaukee, Wis.), and 1 part of polyvinyl alcohol (Celvol 425from Celanese Corporation) dissolved in a 1:1 weight ratio mixture ofisopropanol and water. Upon adding the mixture, pores of less than 10microns in diameter were formed within the pores of the nickel foam, inwhich the sulfur was deposited.

An electrochemical cell including the cathode was assembled for testing.Lithium metal (>99.9% Li, 2 mil thick foil) was used as the anode. Theelectrolyte included 14 parts of lithium bis(trifluoromethane sulfonyl)imide and 4 parts lithium nitrate in a 1:1 weight ratio mixture of1,3-dioxolane and dimethoxyethane. The electrolyte included a watercontent of less than 50 ppm. A 9-micron SETELA porous separator was alsoused.

The above components were assembled into a layered structure ofcathode/separator/anode, which was folded in half to make a bicell. Thebicell was placed in a foil pouch with approximately 0.4 grams of aliquid electrolyte. After storing for 24 hours, half of the cells weretested without compression, and the other half were compressed betweentwo parallel plates at a pressure of 98 Newtons/cm² (about 10kg-force/cm²). The liquid electrolyte filled the void areas of theseparator and cathode to form prismatic cells with an electrode area ofabout 33 cm². Discharge-charge cycling was performed at 13.7 mA and 7.8mA, respectively. The discharge cutoff voltage was 1.7V and the chargecutoff voltage was 2.5V. FIG. 10 includes a plot of specific dischargecapacity as a function of the number of charge-discharge cycles forelectrochemical cells comprising the cathodes fabricated in thisexample. The nickel foam electrodes continued to exhibit relatively highdischarge capacities, even after 40 charge-discharge cycles. Theapplication of 98 Newtons/cm² (about 10 kg-force/cm³) of pressure to thecells led to more consistent cycling performance after about 30 cycles.The use of nickel foam and the application of pressure led to reducedfade rates and extended cycle life. In addition, the rate ofpolarization increase was much slower for the nickel foam cells,especially when pressure was applied.

Comparative Example 3

In this example, a cathode was prepared by coating a mixture of 75 partsof elemental sulfur, 20 parts of Printex® XE-2, 4 parts graphite powder,and 1 part of polyvinyl alcohol dissolved in a 1:1 weight ratio mixtureof isopropanol and water onto a 7-micron thick, conductive carbon coatedaluminum foil substrate. After drying, the coated cathode active layerthickness was about 90 microns. Cells were assembled and tested asoutlined in Example 3. Cycling results are summarized in FIG. 10. Thecell comprising the cathode deposited on the aluminum foil substrateexhibited relatively lower specific discharge capacity relative to thecell comprising the nickel foam cathode.

Example 4

This example describes the fabrication and testing of electrochemicalcells comprising sintered nickel cathodes. Cells with sintered nickelcathodes were prepared using Inco filamentary nickel powder type 255(Inco Special Products). The nickel particles had an apparent density of0.5 to 0.65 g/cm³. In addition, the particles had diameters of betweenabout 1 micron and about 100 microns, with a median diameter of around20 microns. The nickel powder was suspended in acetone, a relativelyvolatile liquid, by vigorously mixing the powder and the suspensionfluid to produce a slurry. The slurry was poured into a crucible, andthe slurry was smoothened to distribute the nickel powder evenly andflatly across the bottom surface of the crucible. The volatilesuspension fluid was then allowed to evaporate at room temperature,leaving behind a relatively ordered array of nickel particles.

At this point the nickel powder was ready for sintering. The sinteringprocess was conducted in a reducing atmosphere comprising 95% nitrogenand 5% hydrogen. The nickel powder was sintered by ramping thetemperature to 800° C. at a rate of 5° C./min, holding for 10 minutes,and allowing the samples to furnace cool with the heating elementsturned off. The final sintered structure had a thickness of about 250microns, with a pore size distribution centered at about 15 microns.

Sulfur was then added to the sintered nickel porous support structure.To incorporate the sulfur, an oil bath was prepared and heated to 85° C.A beaker containing toluene saturated with sulfur was placed in the bathand allowed to come to equilibrium. To ensure a saturated solution asmall amount of sulfur was maintained in solid form as a second phase inthe beaker, by adding sulfur to the toluene as necessary. Toluene wasadded to the beaker as necessary to maintain nearly the same volume oftoluene in the beaker at all times. Each time a significant addition ofreagent (sulfur or toluene) was added, the system was allowed to come toequilibrium. The nickel electrodes were dipped into the beaker withsulfur saturated toluene, and dried with an argon stream. Once all theelectrodes in a batch were dipped, they were baked in a vacuum oven at80° for several hours (anywhere from 1 to overnight ˜14, with 3-4 beingthe most common, appeared to have no effect as long as toluene smell wasnot present when the oven was opened). The electrodes were weighed andcompared with pre-dipping weight to determine the amount of sulfurpresent. If the amount of sulfur was below the desired amount thedipping was repeated. If the amount of sulfur was above the desiredamount the electrodes were quickly dipped in pure toluene, then bakedaccording to the previous procedure. All the electrodes were loaded withbetween 1.5 and 2 mg S₈/cm². The porosity of the final structure wassubstantially the same as the nickel once the sulfur was dissolved.

An electrochemical cell including the cathode was assembled for testing.The anode included a vapor deposited lithium film 26 microns inthickness. The electrolyte included 8 parts of lithiumbis(trifluoromethane sulfonyl) imide and 4 parts lithium nitrate in a1:1 weight ratio mixture of 1,3-dioxolane and dimethoxyethane. Theelectrolyte included a water content of less than 50 ppm. A 16-micronSETELA porous separator was also used. The above components wereassembled into a layered structure of single sided anode/separator/2×(2sided cathode/separator/2×anode back to back/separator)/2 sidedcathode/separator/single sided anode. This flat cell was placed in afoil pouch with approximately 0.62 grams of a liquid electrolyte. Afterstoring for 24 hours the cells were compressed between two parallelplates at a pressure of 98 Newtons/cm² (about 10 kg-force/cm²). Theliquid electrolyte filled the void areas of the separator and cathode toform flat cells with an electrode area of about 99.441 cm².Discharge-charge cycling was performed at 40 mA and 25 mA, respectively.The discharge cutoff voltage was 1.7V and the charge cutoff voltage was2.5V

FIG. 11 includes a plot of the percentage capacity of the tested cellsas a function of C-rate. The cells cycled normally until the 15^(th)discharge when standard rate testing was completed.

Electrochemical cells were fabricated using milestone cathodes forcomparison purposes. The milestone cathodes were made essentially asdescribed in Comparative Example 1, except in this case, the cathodesincluded a 55/20/20/4 mixture of sulfur/XE-2/Vulcan XC72R/PVOH. As canbe seen in FIG. 11, the cells including the sintered nickel cathodesexhibited a higher percentage capacity at higher rates relative to thecells with milestone cathodes.

Example 5

This example describes the fabrication and testing of electrochemicalcells comprising cathodes fabricated using a polymeric porous supportstructure. The polymeric porous support structure was produced bycombining a solution of polyvinyl alcohol (PVA) with ammoniumbicarbonate as a blowing agent, Vulcan carbon, TIMCAL Ks6 graphite, andcarbon fibers were added to the solution of PVA to increase theelectrical conductivity and act as reinforcing agents to improve themechanical properties of the PVA matrix.

The ammonium bicarbonate was pre-milled in an attritor mill to reducethe particle size to the 1 to 2 micron range. Isopropyl alcohol (IPA)was used as a carrier solvent during this milling and was vacuumfiltered from the milled ammonium bicarbonate. To remove the finalamounts of IPA, the ammonium bicarbonate was allowed to dry in an openpan over night. During this overnight drying about 20% of the ammoniumbicarbonate was lost to sublimation.

To prepare the final slurry, a solution containing Vulcan XC72R Carbonand Timcal KS6 graphite (6 micron diameter platelets) was milled with asoluble binder solution of PVOH in water, IPA and2-(2-ethoxyethoxy)ethanol (i.e., dowanol; Dow Chemical) solvents. Thismilled solution is designated as VKC2.

In a second milling step, the VKC2 solution was milled for 20 minutes ina attritor mill with Polygraff PR-24 carbon fibers (Pyrograf Products,Inc., 8 micron diameter, 100-150 micron length) and a small amount ofadditional water. Water was added to improve the adhesion of the foamedprimer to the aluminum substrate (the same type of aluminum foilsubstrate described in Example 1). The pre-milled ammonium bicarbonatewas then added at a ratio of 8 parts ammonium bicarbonate to one part,by weight, of the original primer solids. This final mixture was thenmilled for 10 minutes before being discharged from the attritor mill.

To further reduce the final pore sizes formed by the ammoniumbicarbonate, the VKC2/fiber/ammonium bicarbonate mixture was passed thrua Micro-fluidizer. A single 400 micron chamber was used, and thedischarge pressure was set to 5 kpsi.

One the same day that it was prepared, the slurry was coated onto analuminum substrate using a slot die. The coating was dried in a fourzone, air convection oven (MEGTEC Systems, DePere, Wis.). Thetemperatures of each zone were controlled between 25° C. and about 85°C. to allow of the formation of the pores in the final cathode structureand control the brittleness/adhesion of the cast slurry.

The thickness of the dried, porous polymer matrix prior to compressionwas about 216.7 microns. Upon applying a force of about 98 Newtons/cm²(about 10 kg_(f)/cm²), the polymer matrix thickness was about 112.1microns. The weight of the polymer matrix was about 1.064 mg/cm². Thedibutyl phthalate (DBP) available void space was measured by placing aweighed sample in a bag with an excess amount of DBP to saturate thesample, and re-weighing the resulting saturated sample. The DFPavailable void space was about 0.0038 cm³/cm² per side, which wassignificantly larger than the 0.0015 cm³/cm² required for 1.85 mgS₈/cm².

BET surface area measurements of the polymer matrix indicated that theavailable surface area was about 39 m²/g.

FIG. 12 includes a plot of the polymer matrix thickness as a function ofthe applied pressure (in kg_(f)/cm², which can be converted toNewtons/cm² by multiplying by about 9.8). Three samples were tested. Theapplied force was increased from 0 to 20 kg_(f)/cm², for a total of fourcycles per sample (labeled #1, #2, #3, and #4 in FIG. 12). As the forcewas applied, the thickness of the sample was measured. After the initialcycle, the thickness of each sample returned to only about 45% of itsoriginal thickness. As the samples were exposed to the forces, the DBPuptake of the foam did not vary significantly before and after initialcompression. The data reported in this example was taken after initialcompression.

After formation of the conductive polymer matrix, sulfur was added bydipping the polymer matrix into a hot bath of toluene saturated withsulfur. An electrochemical cell including the cathode was assembled fortesting. Lithium metal (>99.9% Li, 2 mil thick foil from Chemetall-FooteCorp., Kings Mountain, N.C.) was used for the anode. The electrolyteincluded 8 parts of lithium bis(trifluoromethane sulfonyl) imide,(lithium imide available from 3M Corporation, St. Paul, Minn.), 3.8parts lithium nitrate (available from Aldrich Chemical Company,Milwaukee, Wis.), 1 part guanidine nitrate (also available from AldrichChemical Company, Milwaukee, Wis.) and 0.4 parts pyridine nitrate(synthesized in-house from pyridine and nitric acid) in a 1:1 weightratio mixture of 1,3-dioxolane and dimethoxyethane. The electrolyteincluded a water content of less than 50 ppm. A porous separatorcomprising 9-1 μm SETELA (a polyolefin separator available from TonenChemical Corporation, Tokyo, Japan, and from Mobil Chemical Company,Films Division, Pittsford, N.Y.) was included between the anode and thecathode. The dual sided cathode was wrapped with the separator and anodefoil and then placed in a foil pouch. 0.42 grams of the liquidelectrolyte are then added to the foil pouch. The liquid electrolytefills the void areas of the separator and cathode to form prismaticcells with an electrode area of about 31.8 cm². After sealing, the cellswere stored for 24 hours. Prior to being placed on test the cells arecompressed between two parallel plates at a pressure of 98 Newtons/cm²(about 10 kg_(f)/cm²). Charge-discharge cycling was performed at 13.7 mAand 7.8 mA, respectively. The discharge cutoff voltage was 1.7V and thecharge cutoff voltage was 2.5V. The electrochemical cells were exposedto a compressive force of 10 kg_(f)/cm² (about 98 Newtons/cm²). FIG. 13includes a plot of the specific discharge capacity of the cells as afunction of the charge/discharge cycle. The cells exhibited comparableperformance through 20 cycles.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

1. A method of making an electrode for use in an electrochemical cell,comprising: providing a metallic porous support structure comprising aplurality of pores, wherein the plurality of pores of the metallicporous support structure together define a total pore volume, and atleast about 50% of the total pore volume is defined by pores havingcross-sectional diameters of between about 0.1 microns and about 10microns; and depositing an electrode active material comprising sulfurwithin the pores of the metallic porous support structure.
 2. Anelectrode for use in an electrochemical cell, comprising: a metallicporous support structure comprising a plurality of pores; and aplurality of particles comprising an electrode active materialcomprising sulfur substantially contained within the pores of themetallic porous support structure, wherein each particle of theplurality of particles has a maximum cross-sectional dimension; eachparticle of the plurality of particles has a particle volume, and theplurality of particles has a total particle volume defined by the totalof each of the individual particle volumes; and at least about 50% ofthe total particle volume is occupied by particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns.
 3. An electrode for use in an electrochemical cell, comprising:a metallic porous support structure comprising a plurality of pores; anda plurality of particles comprising an electrode active materialcomprising sulfur substantially contained within the pores of themetallic porous support structure, wherein the plurality of particlestogether defines a total quantity of particulate material, and whereinat least about 50% of the total quantity of particulate material is madeup of particles having maximum cross-sectional dimensions of betweenabout 0.1 microns and about 10 microns.
 4. An electrode for use in anelectrochemical cell, comprising: a metallic porous support structurecomprising a plurality of pores; and an electrode active materialcomprising sulfur substantially contained within the pores of themetallic porous support structure, wherein each pore of the plurality ofpores has a pore volume, and the plurality of pores has a total porevolume defined by the total of each of the individual pore volumes; andat least about 50% of the total pore volume is occupied by pores havingcross-sectional diameters of between about 0.1 microns and about 10microns.
 5. An electrode for use in an electrochemical cell, comprising:a metallic porous support structure comprising a plurality of pores; andan electrode active material comprising sulfur substantially containedwithin the pores of the metallic porous support structure, wherein theplurality of pores of the metallic porous support structure togetherdefine a total pore volume, and at least about 50% of the total porevolume is defined by pores having cross-sectional diameters of betweenabout 0.1 microns and about 10 microns.
 6. An electrode as in claim 2,wherein metallic porous support structure comprises at least one of,nickel, copper, magnesium, aluminum, titanium, and scandium.
 7. Anelectrode as in claim 2, wherein the standard deviation of the maximumcross-sectional dimensions of the particles comprising an electrodeactive material comprising sulfur is less than about 50%.
 8. Anelectrode as in claim 4, wherein the standard deviation of thecross-sectional diameters of the pores is less than about 50%.
 9. Anelectrode as in claim 4, wherein the sulfur comprises at least one ofelemental sulfur, polymeric sulfur, inorganic sulfides, inorganicpolysulfides, organic sulfides, organic polysulfides, and sulfur organiccompounds.
 10. An electrode as in claim 9, wherein the sulfur compriseselemental sulfur. 11-15. (canceled)
 16. An electrode as in claim 2,wherein the electrode comprises at least about 20 wt % sulfur.
 17. Anelectrode as in claim 2, wherein the electrode active material occupiesat least about 10% of the accessible pore volume of the porous supportstructure.
 18. An electrode as in claim 2, wherein the electrode has avoid volume of at least about 1 cm³ per gram of sulfur.
 19. An electrodeas in claim 2, wherein an electrochemical cell comprising the electrodeis capable of utilizing at least about 65% of the total sulfur in thecell through at least 1 charge and discharge cycles subsequent to afirst charge and discharge cycle, wherein 100% utilization correspondsto 1672 mAh per gram of sulfur in the electrode.
 20. An electrode as inclaim 2, wherein an electrochemical cell comprising the electrode iscapable of utilizing at least about 65% of the total sulfur in the cellthrough at least 10 charge and discharge cycles subsequent to a firstcharge and discharge cycle, wherein 100% utilization corresponds to 1672mAh per gram of sulfur in the electrode.
 21. An electrode as in claim 2,wherein an electrochemical cell comprising the electrode is capable ofachieving a current density of at least about 100 mA per gram of sulfurin the electrode during at least one charge and discharge cyclesubsequent to a first charge and discharge cycle.
 22. An electrode as inclaim 2, wherein an electrochemical cell comprising the electrode iscapable of achieving a current density of at least about 100 mA per gramof sulfur in the electrode during at least 10 charge and dischargecycles subsequent to a first charge and discharge cycle.
 23. Anelectrode as in claim 2, wherein the porous support structure comprisesa porous continuous structure.
 24. An electrode as in claim 23, whereinthe maximum cross-sectional dimension of the porous continuous structurewithin the electrode is at least about 50% of the maximum crosssectional dimension of the electrode.
 25. An electrode as in claim 2,wherein: the electrode has an external surface area, at least about 50%of the external surface area defines a uniform area with a first averageconcentration of sulfur, and any continuous area that covers about 10%of the uniform area of the external surface includes a second averageconcentration of sulfur that varies by less than about 25% relative tothe first average concentration of sulfur across the uniform area. 26.An electrode as in claim 2, wherein: the electrode has an externalsurface area, at least about 50% of the external surface area defines afirst, continuous area of essentially uniform sulfur distribution, andthe first area has a first average concentration of sulfur, and anycontinuous external surface area that covers about 10% of the first,continuous area of the external surface includes a second averageconcentration of sulfur that varies by less than about 25% relative tothe first average concentration of sulfur across the uniform area. 27.An electrode as in claim 2, wherein: the electrode has a thickness and across-section substantially perpendicular to the thickness, at leastabout 50% of the cross-section defines a uniform area with a firstaverage concentration of sulfur, and any continuous area that coversabout 10% of the uniform area of the cross-section includes a secondaverage concentration of sulfur that varies by less than about 25%relative to the first average concentration of sulfur across the uniformarea.
 28. An electrode as in claim 2, wherein at least about 70% of thetotal volume occupied by particles comprising an electrode activematerial comprising sulfur is occupied by particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns.
 29. An electrode as in claim 2, wherein at least about 80% ofthe total volume occupied by particles comprising an electrode activematerial comprising sulfur is occupied by particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns.
 30. An electrode as in claim 4, wherein at least about 70% ofthe total pore volume is occupied by pores having cross-sectionaldiameters of between about 0.1 microns and about 10 microns.
 31. Anelectrode as in claim 4, wherein at least about 80% of the total porevolume is occupied by pores having cross-sectional diameters of betweenabout 0.1 microns and about 10 microns.
 32. An electrode as in claim 2,wherein the electrode contains less than about 20 wt % binder.
 33. Anelectrode as in claim 2, wherein the ratio of the average maximumcross-sectional dimension of the particles of material within the poroussupport structure to the average cross-sectional diameter of the poreswithin the porous support structure is between about 0.001:1 and about1:1.
 34. A method as in claim 1, wherein providing the metallic poroussupport structure comprises providing a plurality of individual metallicparticles and treating the metallic particles to form a metallic poroussupport structure.
 35. A method as in claim 1, wherein treating themetallic particles to form a porous support structure comprises adheringthe metallic particles.
 36. A method as in claim 1, wherein treating themetallic particles to form a porous support structure comprisessintering the metallic particles.
 37. A method as in claim 1, whereintreating the metallic particles to form a metallic porous supportstructure comprises melting the metallic particles.
 38. A method as inclaim 1, wherein providing the metallic porous support structurecomprises combining a first material and a second material and formingthe pores of the metallic support structure by removing one of thematerials from the combination.
 39. A method as in claim 1, whereinproviding a metallic porous support structure comprises providing apre-fabricated metallic porous support structure.
 40. A method as inclaim 1, wherein providing a metallic porous support structure comprisesfabricating the metallic porous support structure using 3-D printing.41. An electrochemical cell comprising an electrode as in claim 2 and anelectrolyte, wherein the ratio of electrolyte to sulfur, by mass, withinthe electrochemical cell is less than about 6:1.
 42. An electrochemicalcell as in claim 41, wherein the ratio of electrolyte to sulfur, bymass, within the electrochemical cell is less than about 5:1.
 43. Anelectrochemical cell as in claim 41, wherein the ratio of electrolyte tosulfur, by mass, within the electrochemical cell is less than about 4:1.44. An electrochemical cell as in claim 41, wherein the ratio ofelectrolyte to sulfur, by mass, within the electrochemical cell is lessthan about 3:1.
 45. An electrochemical cell as in claim 41, wherein theratio of electrolyte to sulfur, by mass, within the electrochemical cellis less than about 2:1.